---
title: "Synapter2 and synergise2"
author:
- name: Laurent Gatto
affiliation: Computational Proteomics Unit, Cambridge, UK.
- name: Sebastian Gibb
affiliation: Department of Anesthesiology and Intensive Care, University Medicine Greifswald, Germany.
- name: Pavel V. Shliaha
affiliation: Department of Biochemistry and Molecular Biology, University of Southern Denmark, Denmark.
package: synapter
abstract: >
This vignette describes the new functionality implemented version 2.0
of the 'synapter' package. It describes the typical workflow including
the 3D grid search, fragment matching and correction of detector saturation.
bibliography: synapter.bib
output:
BiocStyle::html_document:
toc_float: true
tidy: TRUE
vignette: >
%\VignetteIndexEntry{Synapter2 and synergise2}
%\VignetteEngine{knitr::rmarkdown}
%\VignetteKeywords{Mass Spectrometry, Proteomics, Bioinformatics, quantitative, Ion mobility, label-free}
%\VignetteEncoding{UTF-8}
%\VignettePackage{synapter}
---
```{r environment, echo=FALSE}
suppressPackageStartupMessages(library("synapter"))
suppressPackageStartupMessages(library("synapterdata"))
suppressPackageStartupMessages(library("BiocStyle"))
synobj2RData()
```
```{r include_forword, child="Foreword.md"}
```
```{r include_bugs, child="Bugs.md"}
```
# Introduction
Here we describe the new functionality implemented in *synapter 2.0*. Namely
this vignette covers the utilisation of the new 3D grid search, the fragment
matching, intensity modeling and correction of detector saturation.
# Workflow
The *synapter2* workflow is similar to the old one in *synapter1*.
First it is necessary to use *PLGS* to create the *csv* (and *xml*) files.
Therefore we refer the reader to the default `r Biocpkg("synapter")` vignette,
available [online](https://bioconductor.org/packages/release/bioc/vignettes/synapter/inst/doc/synapter.html)
and with `vignette("synapter", package = "synapter")`.
In contrast to the original workflow the `final_fragment.csv` file for the
identification run and a `Spectrum.xml` file for the quantification run are
needed if the fragment matching should be applied.
Subsequently the original workflow is enhanced by the new
[3D grid search](\#gridsearch) and the [intensity modeling](\#intensitymodel).
Afterwards the [fragment matching](\#fragmentmatching) could be applied.
`r Biocpkg("MSnbase")` [@Gatto2012] is used for further analysis.
The new `r Biocpkg("synapter")` adds
[*synapter*/*PLGS* consensus filtering](\#synapterplgs)
and the [detector saturation correction](\#saturation) for `MSnSet`s.
## Step-by-step workflow
### Create a `Synapter` object
To demonstrate a typical step-by-step workflow we use example data
that are available on http://proteome.sysbiol.cam.ac.uk/lgatto/synapter/data/.
There is also an `synobj2` object in `r Biocexptpkg("synapterdata")` which
contains the same data.
The `Synapter` constructor uses a named `list` of input files. Please note that
we add `identfragments` (`final_fragment.csv`) and
`quantspectra` (`Spectrum.xml`) because we want to apply the fragment matching
later.
```{r create-synobj2-file, echo=FALSE, comment=NA}
cat(readLines(system.file(file.path("scripts", "create_synobj2.R"),
package="synapterdata"), n=13), sep="\n")
```
```{r show-synobj2}
synobj2
```
### Filtering
The first steps in each `r Biocpkg("synapter")` analysis are filtering by
peptide sequence, peptide length, ppm error and *false positive rate*.
Here we use the default values for each method. But the accompanying plotting
methods should be used to find the best threshold:
```{r filtering}
filterUniqueDbPeptides(synobj2,
missedCleavages=0,
IisL=TRUE)
filterPeptideLength(synobj2, l=7)
plotFdr(synobj2)
filterQuantPepScore(synobj2, method="BH",
fdr=0.05)
filterIdentPepScore(synobj2, method="BH",
fdr=0.05)
par(mfcol=c(1, 2))
plotPpmError(synobj2, what="Ident")
plotPpmError(synobj2, what="Quant")
par(mfcol=c(1, 1))
filterQuantPpmError(synobj2, ppm=20)
filterIdentPpmError(synobj2, ppm=20)
plotPepScores(synobj2)
filterIdentProtFpr(synobj2, fpr=0.05)
filterQuantProtFpr(synobj2, fpr=0.05)
```
### Modeling retention time
Next we merge the identified peptides from the identification run and
quantification run and build a
[*LOWESS*](https://en.wikipedia.org/wiki/Local_regression) based retention time
model to remove systematic shifts in the retention times.
Here we use the default values but as stated above the plotting methods should
be used to find sensible thresholds.
```{r rtmodel}
mergePeptides(synobj2)
plotRt(synobj2, what="data")
setLowessSpan(synobj2, span=0.05)
modelRt(synobj2)
par(mfcol=c(1, 2))
plotRtDiffs(synobj2)
plotRt(synobj2, what="model", nsd=1)
par(mfcol=c(1, 1))
plotFeatures(synobj2, what="all", ionmobility=TRUE)
```
### Grid search{#gridsearch}
To find *EMRTS* (exact *m/z*-retention time pairs) we try are running a grid
search to find the best retention time tolerance and *m/z* tolerance that
results in the most correct one-to-one matching in the merged (already
identified) data.
If the identification and quantitation run are HDMS$^E$ data we could
use the new 3D grid search that looks for the best matching in the retention
time, *m/z* and ion mobility (drift time) domain to increase the accuracy.
If one or both datasets are MS$^E$ data it falls back to the traditional 2D grid
search.
```{r gridsearch}
searchGrid(synobj2,
imdiffs=seq(from=0.6, to=1.6, by=0.2),
ppms=seq(from=2, to=20, by=2),
nsds=seq(from=0.5, to=5, by=0.5))
setBestGridParams(synobj2)
findEMRTs(synobj2)
plotEMRTtable(synobj2)
```
### Fragment matching{#fragmentmatching}
For the details of the fragment matching procedure we refer to the
fragment matching vignette that is available
[online](https://bioconductor.org/packages/release/bioc/vignettes/synapter/inst/doc/fragmentmatching.html)
and with `vignette("fragmentmatching", package = "synapter")`.
Briefly we compare the fragments of the identification run with the spectra from
the quantification run and remove entries where there are very few/none common
peaks/fragments between them.
First we starting by removing less intense fragments and peaks.
```{r filterfragments}
filterFragments(synobj2,
what="fragments.ident",
minIntensity=70)
filterFragments(synobj2,
what="spectra.quant",
minIntensity=70)
```
Next we look for common peaks via `fragmentMatching`:
```{r fm}
fragmentMatching(synobj2)
```
We get tables for unique and non-unique matches:
```{r fmperf, results="asis"}
knitr::kable(fragmentMatchingPerformance(synobj2,
what="unique"))
knitr::kable(fragmentMatchingPerformance(synobj2,
what="non-unique"))
```
Subsequently we could filter by minimal accepted common peaks:
```{r filterfm}
filterUniqueMatches(synobj2, minNumber=1)
filterNonUniqueMatches(synobj2, minDelta=2)
filterNonUniqueIdentMatches(synobj2)
```
Finally we rescue EMRTs that are filtered but were identified by *PLGS*:
```{r rescue}
rescueEMRTs(synobj2, method="rescue")
```
### Modeling intensity{#intensitymodel}
In a similar manner as correcting for the retention time drift we correct
systematic errors of the intensity via a
[*LOWESS*](https://en.wikipedia.org/wiki/Local_regression) model.
The function `modelIntensity` has to applied after `findEMRTs`. The model is
build on the merged peptides as it is done for the retention time model. But in
contrast to the retention time model the prediction is necessary for the matched
quantitation data.
```{r intmodel}
plotIntensity(synobj2, what="data")
setLowessSpan(synobj2, 0.05)
modelIntensity(synobj2)
plotIntensity(synobj2, what="model", nsd=1)
```
## `synergise2`
The whole workflow described in the [step-by-step workflow](\#stepbystep) is
wrapped in the `synergise2` function. As side effect it generates a nice
*HTML* report. An example could be found on https://github.com/lgatto/synapter.
```{r synergise2, eval=FALSE}
synobj2 <- synergise2(filenames = inlist,
outputdir = ".")
```
# *synapter*/*PLGS* agreement{#synapterplgs}
For the next steps we need to convert the `Synapter` object into an `MSnSet`.
```{r convert}
msn <- as(synobj2, "MSnSet")
```
Subsequently we look for *synapter*/*PLGS* agreement (this is more
useful for a combined `MSnSet`; see basic `r Biocpkg("synapter")`
[online](https://bioconductor.org/packages/release/bioc/vignettes/synapter/inst/doc/synapter.html#combine)
or with `vignette("synapter", package = "synapter")`).
`synapterPlgsAgreement` adds an agreement column for each sample and counts the
agreement/disagreement in additional columns:
```{r synapterplgs, results="asis"}
msn <- synapterPlgsAgreement(msn)
knitr::kable(head(fData(msn)[, grepl("[Aa]gree",
fvarLabels(msn)),
drop=FALSE]))
```
# Correction of detector saturation{#saturation}
As described in [@Shliaha2013] Synapt G2 devices suffer from detector
saturation. This could be partly corrected by `requantify`. Therefore a
`saturationThreshold` has to be given above that intensity saturation
potentially happens. There are several methods available.
```{r saturation}
msncor <- requantify(msn,
saturationThreshold=1e5,
method="sum")
```
If an `MSnSet` object was requantified using the `"sum"`
requantification method *TOP3* normalisation is not valid anymore
because the most abundant proteins are penalised by removing high intensity
isotopes (for details see `?requantify` and `?rescaleForTop3`). This could be
overcome by calling `rescaleForTop3`:
```{r rescaletop3}
msncor <- rescaleForTop3(before=msn,
after=msncor,
saturationThreshold=1e5)
```
# New functions not covered in this vignette
Since `r Biocpkg("synapter")` 2.0 `makeMaster` supports fragment files as well.
It is possible to create a fragment library that could used for
[fragment matching](\#fragmentmatching) because of the large data this could not
covered in this vignette. An introduction how to create a *master* could be
found in the basic `r Biocpkg("synapter")` vignette, available
[online](https://bioconductor.org/packages/release/bioc/vignettes/synapter/inst/doc/synapter.html)
or with `vignette("synapter", package = "synapter")`. Please find details
about creating a fragment library in `?makeMaster`.
# Session information{#sec:sessionInfo}
All software and respective versions used to produce this document are
listed below.
```{r sessioninfo}
sessionInfo()
```
# References