--- title: "Quantitative features for mass spectrometry data" author: - name: Laurent Gatto package: QFeatures abstract: > This vignette describes the functionality implemented in the QFeatures package. QFeatures provides infrastructure to manage and process quantitative features for high-throughput mass spectrometry assays, including proteomics and metabolomics. output: BiocStyle::html_document: toc_float: true bibliography: QFeatures.bib vignette: > %\VignetteIndexEntry{Quantitative features for mass spectrometry data} %\VignetteEngine{knitr::rmarkdown} %%\VignetteKeywords{Mass Spectrometry, MS, MSMS, Proteomics, Metabolomics, Infrastructure, Quantitative } %\VignetteEncoding{UTF-8} --- ```{r style, echo = FALSE, results = 'asis'} BiocStyle::markdown() ``` ```{r env, message = FALSE, warning = FALSE, echo = FALSE} library("QFeatures") ``` # Introduction The `QFeatures` package provides infrastructure (that is classes to store data and the methods to process and manipulate them) to manage and analyse quantitative features from mass spectrometry experiments. It is based on the `SummarizedExperiment` and `MultiAssayExperiment` classes. Assays in a QFeatures object have a hierarchical relation: proteins are composed of peptides, themselves produced by spectra, as depicted in figure \@ref(fig:featuresplot). Throughout the aggregation and processing of these data, the relations between assays are tracked and recorded, thus allowing users to easily navigate across spectra, peptide and protein quantitative data. ```{r featuresplot, fig.cap = "Conceptual representation of a `QFeatures` object and the aggregative relation between different assays.", echo = FALSE} par(mar = c(0, 0, 0, 0)) plot(NA, xlim = c(0, 12), ylim = c(0, 20), xaxt = "n", yaxt = "n", xlab = "", ylab = "", bty = "n") for (i in 0:7) rect(0, i, 3, i+1, col = "lightgrey", border = "white") for (i in 8:12) rect(0, i, 3, i+1, col = "steelblue", border = "white") for (i in 13:18) rect(0, i, 3, i+1, col = "orange", border = "white") for (i in 19) rect(0, i, 3, i+1, col = "darkgrey", border = "white") for (i in 5:7) rect(5, i, 8, i+1, col = "lightgrey", border = "white") for (i in 8:10) rect(5, i, 8, i+1, col = "steelblue", border = "white") for (i in 11:13) rect(5, i, 8, i+1, col = "orange", border = "white") for (i in 14) rect(5, i, 8, i+1, col = "darkgrey", border = "white") rect(9, 8, 12, 8+1, col = "lightgrey", border = "white") rect(9, 9, 12, 9+1, col = "steelblue", border = "white") rect(9, 10, 12, 10+1, col = "orange", border = "white") rect(9, 11, 12, 11+1, col = "darkgrey", border = "white") segments(3, 8, 5, 8, lty = "dashed") segments(3, 6, 5, 7, lty = "dashed") segments(3, 4, 5, 6, lty = "dashed") segments(3, 0, 5, 5, lty = "dashed") segments(3, 10, 5, 9, lty = "dashed") segments(3, 11, 5, 10, lty = "dashed") segments(3, 13, 5, 11, lty = "dashed") segments(3, 14, 5, 12, lty = "dashed") segments(3, 16, 5, 13, lty = "dashed") segments(3, 19, 5, 14, lty = "dashed") segments(3, 20, 5, 15, lty = "dashed") segments(8, 5, 9, 8, lty = "dashed") segments(8, 8, 9, 9, lty = "dashed") segments(8, 11, 9, 10, lty = "dashed") segments(8, 14, 9, 11, lty = "dashed") segments(8, 15, 9, 12, lty = "dashed") ``` In the following sections, we are going to demonstrate how to create a single-assay `QFeatures` objects starting from a spreadsheet, how to compute the next assays (peptides and proteins), and how these can be manipulated and explored. ```{r loadpkg} library("QFeatures") ``` # Creating `QFeatures` object ```{r loaddfr, echo = FALSE} data(hlpsms) ``` While `QFeatures` objects can be created manually (see `?QFeatures` for details), most users will probably possess quantitative data in a spreadsheet or a dataframe. In such cases, the easiest is to use the `readQFeatures` function to extract the quantitative data and metadata columns. Below, we load the `hlpsms` dataframe that contains data for `r ncol(hlpsms)` PSMs from the TMT-10plex *hyper*LOPIT spatial proteomics experiment from [@Christoforou:2016]. The `ecol` argument specifies that columns 1 to 10 contain quantitation data, and that the assay should be named `psms` in the returned `QFeatures` object, to reflect the nature of the data. ```{r readQFeatures} data(hlpsms) hl <- readQFeatures(hlpsms, ecol = 1:10, name = "psms") hl ``` Below, we see that we can extract an assay using its index or its name. The individual assays are stored as *SummerizedExperiment* object and further access its quantitative data and metadata using the `assay` and `rowData` functions ```{r subsetassay} hl[[1]] hl[["psms"]] head(assay(hl[["psms"]])) head(rowData(hl[["psms"]])) ``` For further details on how to manipulate such objects, refer to the `r BiocStyle::Biocpkg("MultiAssayExperiment")` [@Ramos:2017] and `r BiocStyle::Biocpkg("SummerizedExperiment")` [@SE] packages. As illustrated in figure \@ref(fig:featuresplot), an central characteristic of `QFeatures` objects is the aggregative relation between their assays. This can be obtained with the `aggregateFeatures` function that will aggregate quantitative features from one assay into a new one. In the next code chunk, we aggregate PSM-level data into peptide by grouping all PSMs that were matched the same peptide sequence. Below, the aggregation function is set, as an example, to the mean. The new assay is named *peptides*. ```{r aggregateFeatures1} hl <- aggregateFeatures(hl, "psms", "Sequence", name = "peptides", fun = colMeans) hl hl[["peptides"]] ``` Below, we repeat the aggregation operation by grouping peptides into proteins as defined by the *ProteinGroupAccessions* variable. ```{r aggregateFeatures2} hl <- aggregateFeatures(hl, "peptides", "ProteinGroupAccessions", name = "proteins", fun = colMeans) hl hl[["proteins"]] ``` The sample assayed in a `QFeatures` object can be documented in the `colData` slot. The `hl` data doens't currently possess any sample metadata. These can be addedd as a new `DataFrame` with matching names (i.e. the `DataFrame` rownames must be identical assay's colnames) or can be added one variable at at time, as shown below. ```{r} colData(hl) hl$tag <- c("126", "127N", "127C", "128N", "128C", "129N", "129C", "130N", "130C", "131") colData(hl) ``` # Subsetting One particularity of the `QFeatures` infrastructure is that the features of the constitutive assays are linked through an aggregative relation. This relation is recorded when creating new assays with `aggregateFeatures` and is exploited when subsetting `QFeature` by their feature names. In the example below, we are interested in the Stat3B isoform of the Signal transducer and activator of transcription 3 (STAT3) with accession number P42227-2. This accession number corresponds to a feature name in the *proteins* assay. But this protein row was computed from 8 peptide rows in the *peptides* assay, themselves resulting from the aggregation of 8 rows in the *psms* assay. ```{r stat3} stat3 <- hl["P42227-2", , ] stat3 ``` We can easily visualise this new *QFeatures* object using `ggplot2` once converted into a `data.frame`. ```{r plotstat3} stat3_df <- data.frame(longFormat(stat3)) stat3_df$assay <- factor(stat3_df$assay, levels = c("psms", "peptides", "proteins")) library("ggplot2") ggplot(data = stat3_df, aes(x = colname, y = value, group = rowname)) + geom_line() + geom_point() + facet_grid(~ assay) ``` Below we repeat the same operation for the Signal transducer and activator of transcription 1 (STAT1) and 3 (STAT3) accession numbers, namely P42227-2 and P42225. We obtain a new `QFeatures` instance containing 2 proteins, 9 peptides and 10 PSMS. From this, we can readily conclude that STAT1 was identified by a single PSM/peptide. ```{r stat} stat <- hl[c("P42227-2", "P42225"), , ] stat ``` Below, we visualise the expression profiles for the two proteins. ```{r plotstat} stat_df <- data.frame(longFormat(stat)) stat_df$stat3 <- ifelse(stat_df$rowname %in% stat3_df$rowname, "STAT3", "STAT1") stat_df$assay <- factor(stat_df$assay, levels = c("psms", "peptides", "proteins")) ggplot(data = stat_df, aes(x = colname, y = value, group = rowname)) + geom_line() + geom_point() + facet_grid(stat3 ~ assay) ``` The subsetting by feature names is also available as a call to the `subsetByFeature` function, for use with the pipe operator. ```{r subsetByFeature} library(magrittr) hl %>% subsetByFeature("P42227-2") hl %>% subsetByFeature(c("P42227-2", "P42225")) ``` and possibly ```{r subsetpipe, eval = FALSE} hl %>% subsetByFeature("P42227-2") %>% longFormat() %>% as.data.frame %>% ggplot(aes(x = colname, y = value, group = rowname)) + geom_line() + facet_grid(~ assay) ``` to reproduce the line plot. Finally, a simply `shiny` app allows to explore and visualise the respective assays of a `QFeatures` object. ```{r display, eval = FALSE} display(stat) ``` ```{r heatmapdisplay, results='markup', fig.cap="`QFeatures` interactive interface: heatmap of the peptide assay data.", echo=FALSE, out.width='100%', fig.align='center', fig.wide = TRUE} knitr::include_graphics("./figs/display_hmap.png", error = FALSE) ``` ```{r assaydisplay, results='markup', fig.cap="`QFeatures` interactive interface: quantitative peptide assay data.", echo=FALSE, out.width='100%', fig.align='center', fig.wide = TRUE} knitr::include_graphics("./figs/display_assay.png", error = FALSE) ``` ```{r rowdatadisplay, results='markup', fig.cap="`QFeatures` interactive interface: peptide assay row data", echo=FALSE, out.width='100%', fig.align='center', fig.wide = TRUE} knitr::include_graphics("./figs/display_rowdata.png", error = FALSE) ``` A dropdown menu in the side bar allows the user to select an assay of interest, which can then be visualised as a heatmap (figure \@ref(fig:heatmapdisplay)), as a quantitative table (figure \@ref(fig:assaydisplay)) or a row data table (figure \@ref(fig:rowdatadisplay)). # Filtering QFeatures is assays can also be filtered based on variables in their respective row data slots using the `filterFeatures` function. The filters can be defined using the formula interface or using `AnnotationFilter` objects from the `r BiocStyle::Biocpkg("AnnotationFilter")` package [@AnnotationFilter]. In addition to the pre-defined filters (such as `SymbolFilter`, `ProteinIdFilter`, ... that filter on gene symbol, protein identifier, ...), this package allows users to define arbitrary character or numeric filters using the `VariableFilter`. ```{r varfilter} mito_filter <- VariableFilter(field = "markers", value = "Mitochondrion", condition = "==") mito_filter qval_filter <- VariableFilter(field = "qValue", value = 0.001, condition = "<=") qval_filter ``` These filter can then readily be applied to all assays' row data slots. The `mito_filter` will return all PSMs, peptides and proteins that were annotated as localising to the mitochondrion. ```{r mito_filter} filterFeatures(hl, mito_filter) ``` The `qval_filter`, on the other hand, will only return a subset of PSMs, because the `qValue` variable is only present in the `psms` assays. The q-values are only relevant to PSMs and that variable was dropped from the other assays. ```{r qval_filter} filterFeatures(hl, qval_filter) ``` The same filters can be created using the forumla interface: ```{r formula_filter} filterFeatures(hl, ~ markers == "Mitochondrion") filterFeatures(hl, ~ qValue <= 0.001) ``` # Session information {-} ```{r sessioninfo, echo=FALSE} sessionInfo() ``` # References {-}