Synapter: Class "Synapter"

In lgatto/synapter: Label-free data analysis pipeline for optimal identification and quantitation

Class "Synapter"

Description

A reference class to store, manage and process Synapt G2 data to combine identification and quantitation results.

The data, intermediate and final results are stored together in such a ad-how container called a class. In the frame of the analysis of a set of 3 or 5 data files, namely as identification peptide, a quantitation peptide and a quantitation Pep3D, and identification fragments and quantitation spectra, such a container is created and populated, updated according to the user's instructions and used to display and export results.

The functionality of the synapter package implemented in the Synapter class in described in the Details section below. Documentation for the individual methods is provided in the Methods section. Finally, a complete example of an analysis is provided in the Examples section, at the end of this document.

See also papers by Shliaha et al. for details about ion mobility separation and the manuscript describing the synapter methodology.

Usage

Synapter(filenames, master) ## creates an instance of class 'Synapter'

Arguments

filenames

A named list of file names to be load. The names must be 'identpeptide', 'quantpeptide', 'quantpep3d' and 'fasta' (could be an RDS file created by link{createUniquePeptideDbRds}) and (optional 'identfragments' and 'quantspectra'). identpeptide can be a csv final peptide file (from PLGS) or a saved "MasterPeptides" data object as created by makeMaster if working with master peptide data. To serialise the "MasterPeptides" instance, use the saveRDS function, and file extenstion rds. This master file could contain a fragment library as well. In this case the 'identfragments' argument would be ignored.

master

A logical that defines if the identification file is a master file. See makeMaster for details about this strategy.

Details

A Synapter object logs every operation that is applied to it. When displayed with show or when the name of the instance is typed at the R console, the original input file names, all operations and resulting the size of the respective data are displayed. This allows the user to trace the effect of respective operations.

Loading the data

The construction of the data and analysis container, technically defined as an instance or object of class Synapter, is created with the Synapter constructor. This function requires 4 or 6 files as input, namely, the identification final peptide csv file, the quantitation final peptide csv file, the quantitation Pep3D csv file (as exported from the PLGS software), the fasta file use for peptide identification, and optional the identification fragments csv file and the quantitation spectra xml file. The fasta file ('fasta') could be an RDS file generated by link{createUniquePeptideDbRds}, too. The file names need to be specified as a named list with names 'identpeptide', 'quantpeptide', 'quantpep3d', 'fasta', 'identfragments' and 'quantspectra' respectively. These files are read and the data is stored in the newly created Synapter instance.

The final peptide files are filtered to retain peptides with matchType corresponding to PepFrag1 and PepFrag2, corresponding to unmodified round 1 and 2 peptide identification. Other types, like NeutralLoss_NH3, NeutralLoss_H20, InSource, MissedCleavage or VarMod are not considered in the rest of the analysis. The quantitation Pep3D data is filtered to retain Function equal to 1 and unique quantitation spectrum ids, i.e. unique entries for multiple charge states or isotopes of an EMRT (exact mass-retention time features).

Then, p-values for Regular peptides are computed based on the Regular and Random database types score distributions, as described in Käll et al., 2008a. Only unique peptide sequences are taken into account: in case of duplicated peptides, only one entry is kept. Empirical p-values are adjusted using Bonferroni and Benjamini and Hochberg, 1995 (multtest package) and q-values are computed using the qvalue package (Storey JD and Tibshirani R., 2003 and Käll et al., 2008b). Only Regular entries are stored in the resulting data for subsequent analysis.

The data tables can be exported as csv spreadsheets with the writeIdentPeptides and writeQuantPeptides methods.

Filtering identification and quantitation peptide

The first step of the analysis aims to match reliable peptide. The final peptide datasets are filtered based on the FDR (BH is default) using the filterQuantPepScore and filterIdentPepScore methods. Several plots are provided to illustrate peptide score densities (from which p-values are estimated, plotPepScores; use getPepNumbers to see how many peptides were available) and q-values (plotFdr).

Peptides matching to multiple proteins in the fasta file (non-unique tryptic identification and quantitation peptides) can be discarded with the filterUniqueDbPeptides method. One can also filter on the peptide length using filterPeptideLength.

Another filtering criterion is mass accuracy. Error tolerance quantiles (in ppm, parts per million) can be visualised with the plotPpmError method. The values can be retrieved with getPpmErrorQs. Filtering is then done separately for identification and quantitation peptide data using filterIdentPpmError and filterQuantPpmError respectively. The previous plotting functions can be used again to visualise the resulting distribution.

Filtering can also be performed at the level of protein false positive rate, as computed by the PLGS application (protein.falsePositiveRate column), which counts the percentage of decoy proteins that have been identified prior to the regular protein of interest. This can be done with the filterIdentProtFpr and filterQuantProtFpr methods. Note that this field is erroneously called a false positive rate in the PLGS software and the associated manuscript; it is a false discovery rate.

Merging identification and quantitation peptides

Common and reliable identification and quantitation peptides are then matched based on their sequences and merged using the mergePeptides method.

Retention time modelling

Systematic differences between identification features and quantitation features retention times are modelled by fitting a local regression (see the loess function for details), using the modelRt method. The smoothing parameter, or number of neighbour data points used the for local fit, is controlled by the span parameter that can be set in the above method.

The effect of this parameter can be observed with the plotRt method, specifying what = "data" as parameters. The resulting model can then be visualised with the above method specifying what = "model", specifying up to 3 number of standard deviations to plot. A histogram of retention time differences can be produced with the plotRtDiffs method.

To visualise the feature space plotFeatures could be used. It generates one or two (if ion mobility is available) plots of retention time vs mass and mass vs ion mobility for each data source, namely, Identification data, Quantitation data and Quantitation Pep3D data.

Intensity modelling

Systematic differences between intensities of identification features and quantitation features depending on retention times are modelled by fitting a local regression (see the loess function for details), using the modelIntensity method. The smoothing parameter, or number of neighbour data points used the for local fit, is controlled by the span parameter that can be set in the above method.

The effect of this parameter can be observed with the plotIntensity method, specifying what = "data" as parameters. The resulting model can then be visualised with the above method specifying what = "model", specifying up to 3 number of standard deviations to plot.

Grid search to optimise matching tolerances

Matching of identification peptides and quantitation EMRTs is done within a mass tolerance in parts per million (ppm) and the modelled retention time +/- a certain number of standard deviations. To help in the choice of these two parameters, a grid search over a set of possible values is performed and performance metrics are recorded, to guide in the selection of a 'best' pair of parameters.

The following metrics are computed: (1) the percentage of identification peptides that matched a single quantitation EMRT (called prcntTotal), (2) the percentage of identification peptides used in the retention time model that matched the quantitation EMRT corresponding to the correct quantitation peptide in ident/quant pair of the model (called prcntModel) and (3) the detailed about the matching of the features used for modelling (accessible with getGridDetails) and the corresponding details grid that reports the percentage of correct unique assignments. The detailed grid results specify the number of non matched identification peptides (0), the number of correctly (1) or wrongly (-1) uniquely matched identification peptides, the number of identification peptides that matched 2 or more peptides including (2+) or excluding (2-) the correct quantitation equivalent are also available.

See the next section for additional details about how matching. The search is performed with the searchGrid method, possibly on a subset of the data (see Methods and Examples sections for further details).

The parameters used for matching can be set manually with setPpmError, setRtNsd, setImDiff respectively, or using setBestGridParams to apply best parameters as defined using the grid search. See example and method documentation for details.

Identification transfer: matching identification peptides and quantitation EMRTs

The identification peptide - quantitation EMRT matching, termed identification transfer, is performed using the best parameters, as defined above with a grid search, or using user-defined parameters.

Matching is considered successful when one and only one EMRT is found in the mass tolerance/retention time/ion mobility window defined by the error ppm, number of retention time standard deviations, and ion mobility difference parameters. The values of uniquely matched EMRTs are reported in the final matched dataframe that can be exported (see below). If however, none or more than one EMRTs are matched, 0 or the number of matches are reported.

As identification peptides are serially individually matched to 'close' EMRTs, it is possible for peptides to be matched the same EMRT independently. Such cases are reported as -1 in the results dataframes.

The results can be assess using the plotEMRTtable (or getEMRTtable to retrieve the values) and performace methods. The former shows the number of identification peptides assigned to none (0), exactly 1 (1) or more (> 2) EMRTs. The latter method reports matched identification peptides, the number of (q-value and protein FPR filtered) identification and quantitation peptides. Matched EMRT and quantitation peptide numbers are then compared calculating the synapter enrichment (100 * ( synapter - quant ) / quant) and Venn counts.

Remove Less Intense Peaks

As an additional step it is possible to remove less intense peaks from the spectra and fragment data. Use plotCumulativeNumberOfFragments to plot the number of fragments vs the intensity and to find a good threshold. The filterFragments method could remove peaks if the intensity is below a specified threshold via the minIntensity argument. Set the maxNumber argument to keep only the maxNumber highest peaks/fragments. The what argument controls the data on which the filter is applied. Use what = "fragments.ident" for the identification fragments and what = "spectra.quant" for the quantiation spectra data.

Fragment Matching

After importing fragment and spectra data it is possible to match peaks between the identification fragments and the quantitation spectra using the fragmentMatching method. Use setFragmentMatchingPpmTolerance to set the maximal allowed tolerance for considering a peak as identical. There are two different methods to visualise the results of the fragment matching procedure. plotFragmentMatching plots the fragments and spectra for each considered pair. plotFragmentMatchingPerformance draws two plots. On the left panel you could see the performance of different thresholds for the number of common peaks for unique matches. The right panel visualizes the performance of different differences (delta) of common peaks between the best match (highest number of common peaks) and the second best match in each non unique match group. plotFragmentMatchingPerformance returns the corresponding values invisible or use fragmentMatchingPerformance to access these data. Use filterUniqueMatches and filterNonUniqueMatches to remove unique or non unique matches below the threshold of common peaks respective the difference in common peaks from the MatchedEMRTs data.frame.

Exporting and saving data

The merged identification and quantitation peptides can be exported to csv using the writeMergedPeptides method. Similarly, the matched identification peptides and quantitation EMRTs are exported with writeMatchedEMRTs.

Complete Synapter instances can be serialised with save, as any R object, and reloaded with load for further analysis.

It is possible to get the fragment and spectra data from the identification and quantitation run using getIdentificationFragments respectively getQuantitationSpectra.

Methods

Analysis methods

mergePeptides

signature(object = "Synapter"): Merges quantitation and identification final peptide data, used to perform retention time modelling (see modelRt below).

modelRt

signature(object = "Synapter", span = "numeric"): Performs local polynomial regression fitting (see loess) retention time alignment using span parameter value to control the degree of smoothing.

modelIntensity

signature(object = "Synapter", span = "numeric"): Performs local polynomial regression fitting (see loess) intensity values using span parameter value to control the degree of smoothing.

findEMRTs

signature(object = "Synapter", ppm = "numeric", nsd = "numeric", imdiff = "numeric"): Finds EMRTs matching identification peptides using ppm mass tolerance, nsd number of retention time standard deviations and imdiff difference in ion mobility. The last three parameters are optional if previously set with setPpmError, setRtNsd, setImDiff, or, better, setBestGridParams (see below).

rescueEMRTs

signature(object = "Synapter", method = c("rescue", "copy")): The method parameter defined the behaviour for those high confidence features that where identified in both identification and quantitation acquisitions and used for the retention time model (see mergePeptides). Prior to version 1.1.1, these features were transferred from the quantitation pep3d file if unique matches were found, as any feature ("transfer"). As a result, those matching 0 or > 1 EMRTs were quantified as NA. The default is now to "rescue" the quantitation values of these by directly retrieving the data from the quantification peptide data. Alternatively, the quantitation values for these features can be directly taken from the quantitation peptide data using "copy", thus effectively bypassing identification transfer.

searchGrid

signature(object="Synapter", ppms="numeric", nsds="numeric", imdiffs = "numeric", subset="numeric", n = "numeric", verbose="logical"): Performs a grid search. The grid is defined by the ppm, nsd and imdiffs numerical vectors, representing the sequence of values to be tested. Default are seq(5, 20, 2), seq(0.5, 5, 0.5), seq(0.2, 2, 0.2) respectively. To ignore ion mobility set imdiffs = Inf. subset and n allow to use a randomly chosen subset of the data for the grid search to reduce search time. subset is a numeric, between 0 and 1, describing the percentage of data to be used; n specifies the absolute number of feature to use. The default is to use all data. verbose controls whether textual output should be printed to the console. (Note, the mergedEMRTs value used in internal calls to findEMRTs is "transfer" - see findEMRTs for details).

fragmentMatching

signature(object="Synapter", ppm = "numeric", verbose = "logical": Performs a fragment matching between spectra and fragment data. The ppm argument controls the tolerance that is used to consider two peaks (MZ values) as identical. If verbose is TRUE (default) a progress bar is shown.

Methods to display, access and set data

show

signature(object = "Synapter"): Display object by printing a summary to the console.

dim

signature(x="Synapter"): Returns a list of dimensions for the identification peptide, quantitation peptide, merged peptides and matched features data sets.

inputFiles

signature(object="Synapter"): Returns a character of length 6 with the names of the input files used as identpeptide, quantpeptide, quantpep3d, fasta, identfragments and quantspectra.

getLog

signature(object="Synapter"): Returns a character of variable length with a summary of processing undergone by object.

getGrid

signature(object="Synapter", digits = "numeric"): Returns a named list of length 3 with the precent of total (prcntTotal), percent of model (prcntModel) and detailed (details) grid search results. The details grid search reports the proportion of correctly assigned features (+1) to all unique assignments (+1 and -1). Values are rounded to 3 digits by default.

getGridDetails

signature(object="Synapter"): Returns a list of number of ..., -2, -1, 0, +1, +2, ... results found for each of the ppm/nsd pairs tested during the grid search.

getBestGridValue

signature(object="Synapter"): Returns a named numeric of length 3 with best grid values for the 3 searches. Names are prcntTotal, prcntModel and details.

getBestGridParams

signature(object="Synapter"): Returns a named list of matrices (prcntTotal, prcntModel and details). Each matrix gives the ppm and nsd pairs that yielded the best grid values (see getBestGridValue above).

setBestGridParams

signature(object="Synapter", what="character"): This methods set the best parameter pair, as determined by what. Possible values are auto (default), model, total and details. The 3 last ones use the (first) best parameter values as reported by getBestGridParams. auto uses the best model parameters and, if several best pairs exists, the one that maximises details is selected.

setPepScoreFdr

signature(object="Synapter", fdr = "numeric"): Sets the peptide score false discovery rate (default is 0.01) threshold used by filterQuantPepScore and filterIdentPepScore.

getPepScoreFdr

signature(object="Synapter"): Returns the peptide false discrovery rate threshold.

setIdentPpmError

signature(object="Synapter", ppm = "numeric"): Set the identification mass tolerance to ppm (default 10).

getIdentPpmError

signature(object="Synapter"): Returns the identification mass tolerance.

setQuantPpmError

signature(object="Synapter", ppm = "numeric"): Set the quantitation mass tolerance to ppm (default 10).

getQuantPpmError

signature(object="Synapter"): Returns the quantitation mass tolerance.

setPpmError

signature(object="Synapter", ppm = "numeric"): Sets the identification and quantitation mass tolerance ppm (default is 10).

setLowessSpan

signature(object="Synapter", span = "numeric"): Sets the loess span parameter; default is 0.05.

getLowessSpan

signature(object="Synapter"): Returns the span parameter value.

setRtNsd

signature(object="Synapter", nsd = "numeric"): Sets the retention time tolerance nsd, default is 2.

getRtNsd

signature(object="Synapter"): Returns the value of the retention time tolerance nsd.

setImDiff

signature(object="Synapter", imdiff = "numeric"): Sets the ion mobility tolerance imdiff, default is 0.5.

getImDiff

signature(object="Synapter"): Returns the value of the ion mobility tolerance imdiff.

getPpmErrorQs

signature(object="Synapter", qs = "numeric", digits = "numeric"): Returns the mass tolerance qs quantiles (default is c(0.25, 0.5, 0.75, seq(0.9, 1, 0.01)) for the identification and quantitation peptides. Default is 3 digits.

getRtQs

signature(object="Synapter", qs = "numeric", digits = "numeric"): Returns the retention time tolerance qs quantiles (default is c(0.25, 0.5, 0.75, seq(0.9, 1, 0.01)) for the identification and quantitation peptides. Default is 3 digits.

getPepNumbers

signature(object="Synapter"): Returns the number of regular and random quantitation and identification peptide considered for p-value calculation and used to plot the score densities (see plotPepScores). Especially the difference between random and regular entries are informative in respect with the confidence of the random scores distribution.

setFragmentMatchingPpmTolerance

signature(object="Synapter", ppm = "numeric"): Sets the fragment matching mass tolerance ppm (default is 25).

getFragmentMatchingPpmTolerance

signature(object="Synapter"): Returns the fragment matching mass tolerance in ppm.

showFdrStats

signature(object="Synapter", k = "numeric"): Returns a named list of length 2 with the proportion of identification and quantitation peptides that are considered significant with a threshold of k (default is c(0.001, 0.01, 0.5, 0.1)) using raw and adjusted p-values/q-values.

getEMRTtable

signature(object="Synapter"): Returns a table with the number of 0, 1, 2, ... assigned EMRTs.

performance

signatute(object="Synapter", verbose = TRUE): Returns (and displays, if verbose) the performance of the synapter analysis.

performance2

signatute(object="Synapter", verbose = TRUE): Returns (and displays, if verbose) information about number of missing values and identification source of transfered EMRTs.

fragmentMatchingPerformance

signature(object="Synapter", what = c("unique", "non-unique"): Returns the performance of the fragment matching for unqiue or non-unique matches. The return valus is a matrix with seven columns. The first column ncommon/deltacommon contains the thresholds. Column 2 to 5 are the true positives tp, false positives fp, true negatives tn, false negatives fn for the merged peptide data. The sixth column all shows the corresponding number of peptides for all peptides (not just the merged ones) and the last column shows the FDR fdr for the current threshold (in that row) for the merged data.

Please note that the FDR is overfitted/underestimated because the merged peptides are the peptides from the highest quality spectra were PLGS could easily identify the peptides. The peptides that are not present in the merged data are often of lower quality hence the FDR would be higher by trend.

See plotFragmentMatchingPerformance for a graphical representation.

Filters

filterUniqueDbPeptides

signature(object="Synapter", missedCleavages = 0, IisL = TRUE, verbose = TRUE): This method first digests the fasta database file and keeps unique tryptic peptides. (NOTE: since version 1.5.3, the tryptic digestion uses the cleaver package, replacing the more simplistic inbuild function. The effect of this change is documented in https://github.com/lgatto/synapter/pull/47). The number of maximal missed cleavages can be set as missedCleavages (default is 0). If IisL = TRUE Isoleucin and Leucin are treated as the same aminoacid. In this case sequences like "ABCI", "ABCL" are removed because they are not unqiue anymore. If IisL = FALSE (default) "ABCI" and "ABCL" are reported as unique. The peptide sequences are then used as a filter against the identification and quantitation peptides, where only unique proteotyptic instances (no miscleavage allowed by default) are eventually kept in the object instance. This method also removes any additional duplicated peptides, that would not match any peptides identified in the fasta database.

filterUniqueQuantDbPeptides

signature(object="Synapter", missedCleavages = 0, IisL = TRUE, verbose = TRUE): As filterUniqueDbPeptides for quantitation peptides only.

filterUniqueIdentDbPeptides

signature(object="Synapter", missedCleavages = 0, IisL = TRUE, verbose = TRUE): As filterUniqueDbPeptides for identification peptides only.

filterQuantPepScore

signature(object="Synapter", fdr = "numeric", method = "character"): Filters the quantitation peptides using fdr false discovery rate. fdr is missing by default and is retrieved with getPepScoreFdr automatically. If not set, default value of 0.01 is used. method defines how to performe p-value adjustment; one of BH, Bonferrone or qval. See details section for more information.

filterIdentPepScore

signature(object="Synapter", fdr = "numeric", method = "charactet"): As filterQuantPepScore, but for identification peptides.

filterQuantProtFpr

signature(object="Synapter", fpr = "numeric"): Filters quantitation peptides using the protein false positive rate (erroneously defined as a FPR, should be FDR), as reported by PLGS, using threshold set by fpr (missing by default) or retrieved by getProtFpr.

filterIdentProtFpr

signature(object="Synapter", fpr = "numeric"): as filterQuantProtFpr, but for identification peptides.

filterQuantPpmError

signature(object="Synapter", ppm = "numeric"): Filters the quantitation peptides based on the mass tolerance ppm (default missing) provided or retrieved automatically using getPpmError.

filterIdentPpmError

signature(object="Synapter"): as filterQuantPpmError, but for identification peptides.

filterFragments

signature(object = "Synapter", what = c("fragments.ident", "spectra.quant"), minIntensity = "numeric", maxNumber = "numeric", verbose = "logical"): Filters the spectra/fragment data using a minimal intensity threshold (minIntensity) or a maximal number of peaks/fragments threshold (maxNumber). Please note that the maximal number is transfered to an intensity threshold and the result could contain less peaks than specified by maxNumber. If both arguments are given, the more aggressive one is chosen. Use the what argument to specify the data that should be filtered. Set what = "fragments.ident" for the identification fragment data or what = "spectra.quant" for the quantiation spectra. If verbose is TRUE (default) a progress bar is shown.

filterUniqueMatches

signature(object="Synapter", minNumber = "numeric"): Removes all unique matches that have less than minNumber of peaks/fragments in common. Use fragmentMatchingPerformance(..., what="unique")/ plotFragmentMatchingPerformance (left panel) to find an ideal threshold.

filterNonUniqueMatches

signature(object="Synapter", minDelta = "numeric"): Removes all non unique matches that have a difference between the best match (highest number of common peaks/fragments, treated as true match) and the second best match (second highest number of common peaks/fragments) less than minDelta. For the matches above the threshold only the one with the highest number of common peaks/fragments in each match group is kept. Use fragmentMatchingPerformance(..., what="non-unique")/ plotFragmentMatchingPerformance (right panel) to find an ideal threshold.

filterNonUniqueIdentMatches

signature(object="Synapter"): Removes all non unique identification matches. In rare circumstances (if the grid search parameters are to wide/relaxed or a fragment library is used) it could happen that the searchGrid methods matches a single quantification EMRT to multiple identification EMRTs. This methods removes all these non unique matches.

Plotting

plotPpmError

signature(object="Synapter", what = "character"): Plots the proportion of data against the mass error tolerance in ppms. Depending on what, the data for identification (what = "Ident"), quantitation (what = "Quant") or "both" is plotted.

plotRtDiffs

signature(object="Synapter", ...): Plots a histogram of retention time differences after alignments. ... is passed to hist.

plotRt

signature(object="Synapter", what = "character", f = "numeric", nsd = "numeric"): Plots the Identification - Quantitation retention time difference as a function of the Identification retention time. If what is "data", two plots are generated: one ranging the full range of retention time differences and one focusing on the highest data point density and showing models with various span parameter values, as defined by f (default is 2/3, 1/2, 1/4, 1/10, 1/16, 1/25, 1/50, passed as a numed numeric). If what is "model", a focused plot with the applied span parameter is plotted and areas of nsd (default is x(1, 3, 5) number of standard deviations are shaded around the model.

plotIntensity

signature(object="Synapter", what = "character", f = "numeric", nsd = "numeric"): Plots the (log2) ratio of Identification and Quantitation intensities as a function of the Identification retention time. If what is "data", two plots are generated: one ranging the full range of ratios and one focusing on the highest data point density and showing models with various span parameter values, as defined by f (default is 2/3, 1/2, 1/4, 1/10, 1/16, 1/25, 1/50, passed as a numed numeric). If what is "model", a focused plot with the applied span parameter is plotted and areas of nsd (default is x(1, 3, 5) number of standard deviations are shaded around the model.

plotPepScores

signature(object="Synapter"): Plots the distribution of random and regular peptide scores for identification and quantitation features. This reflects how peptide p-values are computed. See also getPepNumbers.

plotFdr

signature(object="Synapter", method = "character"): Displays 2 plots per identification and quantitation peptides, showing the number of significant peptides as a function of the FDR cut-off and the expected false number of false positive as a number of significant tests. PepFrag 1 and 2 peptides are illustrated on the same figures. These figures are adapted from plot.qvalue. method, one of "BH", "Bonferroni" or "qval", defines what identification statistics to use.

plotEMRTtable

signature(object="Synapter"): Plots the barchart of number or 0, 1, 2, ... assigned EMRTs (see getEMRTtable) .

plotGrid

signature(object="Synapter", what = "character"), maindim = "character": Plots a heatmap of the respective grid search results. This grid to be plotted is controlled by what: "total", "model" or "details" are available. If ion mobility was used in the grid search you can use maindim to decided which dimensions should be shown. maindim could be one of "im" (default), "rt" and "mz". If maindim = "im" a heatmap for each ion mobility threshold is drawn. For maindim = "rt" and maindim you get a heatmap for each retention time respective mass threshold.

plotFeatures

signature(object="Synapter", what = "character", xlim = "numeric", ylim = "numeric", ionmobiltiy = "logical"): Plots the retention time against precursor mass space. If what is "all", three (six if ion mobility is available and ionmobility = TRUE (default is FALSE); three additional plots with precursor mass against ion mobility) such plots are created side by side: for the identification peptides, the quantitation peptides and the quantitation Pep3D data. If what is "some", a subset of the rt/mass space can be defined with xlim (default is c(40, 60)) and ylim (default is c(1160, 1165)) and identification peptide, quantitation peptides and EMRTs are presented on the same graph as grey dots, blue dots and red crosses respectively. In addition, rectangles based on the ppm and nsd defined tolerances (see setPpmError and setNsdError) are drawn and centered at the expected modelled retention time. This last figure allows to visualise the EMRT matching.

plotFragmentMatching

signature(object = "Synapter", key = "character", column = "character", verbose = "logical", ...): Plots two spectra and fragments against each other. Please see plotFragmentMatching for details.

plotFragmentMatchingPerformance

signature(object = "Synapter", showAllPeptides = FALSE): Creates two plots. The left panel shows the performance of filtering the unique matches of the merged peptides using a different number of common peaks. The right panel shows the performance of filtering the non unique matches of the merged peptides using different differences (delta) in common peaks/fragments. These differences (delta) are calculated between the match with the highest number of common peaks/fragments and the second highest one. Use filterUniqueMatches and filterNonUniqueMatches to filter the MatchedEMRT data.frame using one of these thresholds. This function returns a list with two named elements (unqiue and nonunqiue invisibly. These are the same data as return by fragmentMatchingPerformance.

Use showAllPeptides=TRUE to add a line for all peptides (not just the merged onces) to both plots.

plotCumulativeNumberOfFragments

signature(object = "Synapter", what = c("fragments.ident", "spectra.quant")): Plots the cumulative number of the fragments/peaks vs their intensity (log10 scaled). Use the what argument to create this plot for the identification fragments (what = "fragments.quant") or the the quantitation spectra (what = "spectra.quant").

Exporters

writeMergedPeptides

signature(object="Synapter", file = "character", what = "character", ...): Exports the merged peptide data to a comma-separated file (default name is "Res-MergedPeptides.csv").

writeMatchedEMRTs

signature(object="Synapter", file = "character", ...): As above, saving the matched EMRT table.

writeIdentPeptides

signature(object="Synapter", file = "character", ...): As above, exporting the identification peptide data.

writeQuantPeptides

signature(object="Synapter", file = "character", ...): A above, exporting the quantitation peptide data.

getIdentificationFragments

signature(object="Synapter"): returns the identification fragments as MSnExp.

getQuantitationSpectra

signature(object="Synapter"): returns the quantitation spectra as MSnExp.

Other

as(, "MSnSet")

signature(x = "Synapter"): Coerce object from Synapter to MSnSet class.

validObject

signature(object = "Synapter"): Test whether a given Synapter object is valid.

updateObject

signature(object = "Synapter"): Updates an old Synapter object.

Author(s)

Laurent Gatto [e-mail]

References

Käll L, Storey JD, MacCoss MJ, Noble WS Posterior error probabilities and false discovery rates: two sides of the same coin. J Proteome Res. 2008a Jan; 7:(1)40-4

Bonferroni single-step adjusted p-values for strong control of the FWER.

Benjamini Y. and Hochberg Y. Controlling the false discovery rate: a practical and powerful approach to multiple testing. J. R. Statist. Soc. B., 1995, Vol. 57: 289-300.

Storey JD and Tibshirani R. Statistical significance for genome-wide experiments. Proceedings of the National Academy of Sciences, 2003, 100: 9440-9445.

Käll, Storey JD, MacCoss MJ, Noble WS Assigning significance to peptides identified by tandem mass spectrometry using decoy databases. J Proteome Res. 2008b Jan; 7:(1)29-34

Improving qualitative and quantitative performance for MSE-based label free proteomics, N.J. Bond, P.V. Shliaha, K.S. Lilley and L. Gatto, Journal of Proteome Research, 2013, in press.

The Effects of Travelling Wave Ion Mobility Separation on Data Independent Acquisition in Proteomics Studies, P.V. Shliaha, N.J. Bond, L. Gatto and K.S. Lilley, Journal of Proteome Research, 2013, in press.

Trypsin cleavage:

Glatter, Timo, et al. Large-scale quantitative assessment of different in-solution protein digestion protocols reveals superior cleavage efficiency of tandem Lys-C/trypsin proteolysis over trypsin digestion. Journal of proteome research 11.11 (2012): 5145-5156. http://dx.doi.org/10.1021/pr300273g

Rodriguez, Jesse, et al. Does trypsin cut before proline?. Journal of proteome research 7.01 (2007): 300-305. http://dx.doi.org/10.1021/pr0705035

Brownridge, Philip, and Robert J. Beynon. The importance of the digest: proteolysis and absolute quantification in proteomics. Methods 54.4 (2011): 351-360. http://dx.doi.org/10.1016/j.ymeth.2011.05.005

cleaver's rules are taken from: http://web.expasy.org/peptide_cutter/peptidecutter_enzymes.html#Tryps

Examples

library(synapter) ## always needed

## Not run: 
## (1) Construction - to create your own data objects
synapterTiny <- Synapter()

## End(Not run)

## let's use synapterTiny, shipped with the package
synapterTinyData() ## loads/prepares the data
synapterTiny ## show object

## (2) Filtering
## (2.1) Peptide scores and FDR

## visualise/explore peptide id scores
plotPepScores(synapterTiny)
getPepNumbers(synapterTiny)

## filter data
filterUniqueDbPeptides(synapterTiny) ## keeps unique proteotypic peptides
filterPeptideLength(synapterTiny, l = 7) ## default length is 7

## visualise before FDR filtering
plotFdr(synapterTiny)

setPepScoreFdr(synapterTiny, fdr = 0.01) ## optional
filterQuantPepScore(synapterTiny, fdr = 0.01) ## specifying FDR
filterIdentPepScore(synapterTiny) ## FDR not specified, using previously set value

## (2.2) Mass tolerance
getPpmErrorQs(synapterTiny)
plotPpmError(synapterTiny, what="Ident")
plotPpmError(synapterTiny, what="Quant")

setIdentPpmError(synapterTiny, ppm = 20) ## optional
filterQuantPpmError(synapterTiny, ppm = 20)
## setQuantPpmError(synapterTiny, ppm = 20) ## set quant ppm threshold below
filterIdentPpmError(synapterTiny, ppm=20)

filterIdentProtFpr(synapterTiny, fpr = 0.01)
filterQuantProtFpr(synapterTiny, fpr = 0.01)

getPpmErrorQs(synapterTiny) ## to be compared with previous output

## (3) Merge peptide sequences
mergePeptides(synapterTiny)

## (4) Retention time modelling
plotRt(synapterTiny, what="data")
setLowessSpan(synapterTiny, 0.05)
modelRt(synapterTiny) ## the actual modelling
getRtQs(synapterTiny)
plotRtDiffs(synapterTiny)
## plotRtDiffs(synapterTiny, xlim=c(-1, 1), breaks=500) ## pass parameters to hist()
plotRt(synapterTiny, what="model") ## using default nsd 1, 3, 5
plotRt(synapterTiny, what="model", nsd=0.5) ## better focus on model

plotFeatures(synapterTiny, what="all")
setRtNsd(synapterTiny, 3)     ## RtNsd and PpmError are used for detailed plot
setPpmError(synapterTiny, 10) ## if not set manually, default values are set automatically
plotFeatures(synapterTiny, what="some", xlim=c(36,44), ylim=c(1161.4, 1161.7))
## best plotting to svg for zooming

set.seed(1) ## only for reproducibility of this example

## (5) Grid search to optimise EMRT matching parameters
searchGrid(synapterTiny,
           ppms = 7:10,  ## default values are 5, 7, ..., 20
           nsds = 1:3,   ## default values are 0.5, 1,  ..., 5
           subset = 0.2) ## default is 1
## alternatively, use 'n = 1000' to use exactly
## 1000 randomly selected features for the grid search
getGrid(synapterTiny)  ## print the grid
getGridDetails(synapterTiny)  ## grid details
plotGrid(synapterTiny, what = "total")   ## plot the grid for total matching
plotGrid(synapterTiny, what = "model")   ## plot the grid for matched modelled feature
plotGrid(synapterTiny, what = "details") ## plot the detail grid
getBestGridValue(synapterTiny)  ## return best grid values
getBestGridParams(synapterTiny) ## return parameters corresponding to best values
setBestGridParams(synapterTiny, what = "auto") ## sets RtNsd and PpmError according the grid results
## 'what' could also be "model", "total" or "details"
## setPpmError(synapterTiny, 12) ## to manually set values
## setRtNsd(synapterTiny, 2.5)

## (6) Matching ident peptides and quant EMRTs
findEMRTs(synapterTiny)
plotEMRTtable(synapterTiny)
getEMRTtable(synapterTiny)
performance(synapterTiny)
performance2(synapterTiny)

## (7) Exporting data to csv spreadsheets
writeMergedPeptides(synapterTiny)
writeMergedPeptides(synapterTiny, file = "myresults.csv")
writeMatchedEMRTs(synapterTiny)
writeMatchedEMRTs(synapterTiny, file = "myresults2.csv")
## These will export the filter peptide data
writeIdentPeptides(synapterTiny, file = "myIdentPeptides.csv")
writeQuantPeptides(synapterTiny, file = "myQuantPeptides.csv")
## If used right after loading, the non-filted data will be exported

lgatto/synapter documentation built on Sept. 28, 2022, 6:53 a.m.