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BENPPy: BayesENproteomics in Python

Python implementation of BayesENproteomics.

version 2.7.18

BayesENproteomics fits user-specified regression models of arbitrary complexity to accurately model protein and post-translational modification fold changes in label-free proteomics experiments. BayesENproteomics uses Elastic Net regularization and observation weighting based on residual size and peptide identification confidence, implemented via MCMC sampling from conditional distributions, to prevent overfitting.

If you find this method useful, please cite our manuscript.

Additonal features over BayesENproteomics proof-of-concept Matlab implementation:

  • User-customised regression models to facilitate analysis of complex (or simple) experimental setups.
  • Protein and PTM run-level quantification (in addition to linear model fold change estimates) based on summation of user-specified effects.
  • No requirement to specify which PTMs to look for, BENPPy will automatically quantify any PTMs it can find (ideal for quantifying results obtained from unconstrained peptide search engines).
  • MaxQuant and PEAKS compatibility.
  • Control group error propagation when calculating significance (Welch's t-test), if desired.
  • Option to use Bayes Factors instead of p-values, if desired.
  • Option to run multiple MCMC in parallel for each protein - may improve numerical stability and reproducibility.
  • Specify fixed and random effects.

Required libraries

BENPPy is tested on Python 3.6 and has the following dependencies:

  • NumPy
  • SciPy
  • Pandas
  • Matplotlib
  • Sci-Kit Learn

Installation

Assuming a standard Python installation with pip and git, BENPPy can be installed via:

pip install git+https://github.com/VenkMallikarjun/BENPPy

BENPPy can be imported by:

import BENPPy as bp

Usage

1. Create a new BayesENproteomics instance (new_instance) using:

::

new_instance = bp.BayesENproteomics(output_name,    # String specifying a folder name within your working directory where output files will be stored (folder will be created if it doesn't already exist).
                                    form            # Can be either 'progenesis' (default), 'peaks' or 'maxquant' to specify the peptide list input format.
                                    update_databases, # Boolean denoting whether to download new versions of UniProt and Reactome, defaults to True.
                                    )

2. Start the analysis with:

::

new_instance.doAnalysis(normalisation_peptides, # String specifying name of .csv file in format specified by 'form' containing peptides to be used for normalisation (can be the same as 'experimental_peptides'). Assumes values are not logged.
                        experimental_peptides,  # String specifying name of .csv file in format specified by 'form' containing peptides to be used in quantitation. Assumes values are not logged.
                        organism,               # String specifying organism name. Can be 'human', 'mouse' or any UniProt proteome ID.
                        othermains_bysample,    # String specifying name of .csv file specifying additional main effects, with levels specified for each sample, to be included in model fitting. Defaults to ''.
                        othermains_bypeptide,   # String specifying name of .csv file specifying additional main effects, with levels specified for each peptide, to be included in model fitting. Defaults to ''.
                        otherinteractors,       # Dictionary specifying additional interacting parameters (E.g. {'Interactor1':'Interactor2','Interactor1':'Interactor3'}). Order of interactors does not matter. Defaults to {'Peptide':'Group'}. Specify {} to remove default peptide:treatment interactions.
                        regression_method,      # Can be either 'protein' (default) to fit separate models for each protein, or 'dataset' to fit a single model for entire dataset (depreciated).
                        normalisation_method,   # Can be either 'median' (default) to normalise by median subtraction following log transformation, or 'none' to perform no normalisation.
                        pepmin,                 # Scalar specifying minimum number of peptides to fit a model for a protein. Proteins with fewer than pepmin peptides will be ignored. Defaults to 3.
                        ProteinGrouping,        # If ProteinGrouping is set to True, will treat all proteins with the same gene name as a single entity using all available peptides, otherwise each one will be calculated separately.
                        peptide_BHFDR,          # Scalar FDR cutoff employed to filter peptides before analysis. Defaults to 0.2.
                        nDB,                    # Scalar denoting number of databases used. Only modify this value if using earlier versions of Progenesis (<3.0). Defaults to 1.
                        incSubject,             # Bool denoting whether or not to include subject/run terms in model to be fit. Defaults to False.
                        subQuantadd,            # List of strings denoting which parameters to add to the 'Treatment' values to give subject-level quantification. Defaults to [''].
                        random_effects,         # List of strings denoting which effects will be sampled from a Gaussian with a mean of 0. E.g. ['Peptide','Donor']. Defaults to ['All'].
                        nChains,                # Integer denoting how many chains to run for each protein. Chains are run in parallel. Defaults to 3.
                        impute,                 # String denoting which imputation method to use. Accepts either 'ami' (Adaptive Multiple Imputation; default) or 'dgd' (Down-shifted Gaussian Distribution imputation).
                        reassign_unreviewed,    # Bool denoting whether to reassign peptides from unreviewed proteins to most abundant (by peptide number) reviewed protein if sequences match. Defaults to True.
                        continuousvars          # List denoting which variables contained in othermains_bysample or othermains_bypeptide are continuous. By default all variables are encoded as categorical.
                        )
  • If form = 'progenesis' than experimental_peptides is simply the peptide (ion)-level output from Progenesis QI, both experimental_peptides and normalisation_peptides must be formatted the same. Do not include spectral counts.
  • If form = 'maxquant' than experimental_peptides is a list containing the MaxQuant Peptides.txt first and any [PTM]Sites.txt (E.g. ['Peptides.txt','Oxidation (M)Sites.txt','Acetylation (K)Sites.txt']) and normalisation_peptides takes the format of 'Peptides.txt'.
  • If form = 'peaks' then experimental peptides is a list containing the exported protein-peptide.csv lists from PEAKS-LFQ, PEAKS-DB, PEAKS-PTM and PEAKS-SPIDER outputs. E.g.['protein-peptidesLFQ.csv','protein-peptidesPEAKSDB.csv','protein-peptidesPEAKSPTM.csv','protein-peptidesSPIDER.csv']. As BENPPy will perfrom FDR filtering on peptide lists, it is important that lists exported from PEAKS are unfiltered. normalisation peptides takes the same format except 'protein-peptidesLFQ' would be replaced with an identically formatted list of peptides to be used for normalisation.
  • reassign_unreviewed should be disabled when analysing complete mixed species datasets (e.g. xenograft models) to avoid peptides from unreviewed proteins in one species being incorrectly assigned to reviewed proteins in the other species. If analysing the species separately (i.e. taking separate lists of species-unique peptides), reassign_unreviewed can be left enabled.

** For MaxQuant and PEAKS files, ensure that the identifier for each sample is the same for samples belonging to the same treatment group. E.g. For MaxQuant in peptides.txt or PEAKS in protein-peptidesLFQ.csv, a list of headers for 6 columns of peptide intensites corresponding to 6 different samples from 2 treatment groups should be, for instance: ['IntensityGroup1','IntensityGroup1','IntensityGroup1','IntensityGroup2','IntensityGroup2','IntensityGroup2']. Alternatively, the .csv file specified in othermains_bysample can also have a "Group" column to specify experimental groups without having to modify original peptide lists.

*** Note that as of 13/06/2019, I have noticed that setting nChains to > 1 can cause the program to hang indefinitely when run in Spyder. The current work-around for this is to run it in an external terminal if nChains > 1 is required.

2.1 Customised models

By default BENPPy fits the following regularised model for each protein:

log_2(MS1 Intensity) = T + P + T*P + e

Where T and P are treatment and peptide effects recpectively and T*P represents the interaction between them, with e representing the error term.

These basic models can be extended by the user as desired by the othermains_bysample and othermains_bypeptide parameters. These are specified as strings containing the names of .csv files which contain columns of categorical identifiers with headers in the first row. Examples of how to specify othermains_bysample and othermains_bypeptide can be found in the examples folder (testsamplemains.csv and testpeptidemains.csv, respectively). Additional interaction effects can be specified by a dictionary in the otherinteractors parameter.

BENPPy will perform both protein-, PTM- (if PTMs are in your dataset) and pathway-level quantification, exporting the respective results as .csv files as each step finishes.

3. Inspect results:

After doAnalysis finishes there will be several new properties added to the instance created in step 1 (and exported as .csv files to the folder specified by output_name).

Preliminary analysis properties - input data

  • new_instance.input_table provides information about parameters used in analysis.
  • new_instance.peptides_used lists peptides that were used in subsequent analysis.
  • new_instance.allValues gives all values (observed and average imputed) for each peptide.
  • new_instance.missing_peptides_idx Boolean array denoting where missing values are in new_instance.allValues.
  • new_instance.UniProt UniProt database used at time of analysis.
  • new_instance.longtable long-form vector table used in creation of design matrices.

Summary fold changes

  • new_instance.protein_summary_quant protein-level log2 abundances.
  • new_instance.ptm_summary_quant ptm-level log2 abundances.
  • new_instance.pathway_summary_quant pathway-level log2 abundances.
  • new_instance.other_summary_quant protein-level log2 effect sizes for non-treatment variables

Subject-level quantifications

If subQuantadd arguement is used when doAnalysis is called, or if incSubject = True protein and ptm subject/run-level quantification will be provided in new_instance.protein_subject_quant and new_instance.ptm_subject_quant, respectively. At the moment, this will only work if the dataset is balanced (i.e. same numbers of samples per group).

4. Quality-control plots:

  • new_instance.boxplots() will create boxplots of logged protein-, PTM-, peptidoform and pathway-level abundances. Extremely large values indicate potential overfitting. Tightening (decreasing) the peptide FDR threshold (peptide_BHFDR arguement in doAnalysis) or decreasing model complexity may improve overfitting.
  • If contrasts have been made (see step 5), new_instance.volcanoes(plot_type = 'protein',residue = 'any') will create protein-level volcano plots (log2(fold changes) vs. -log10(BHFDR)). plot_type can also be 'ptm' to show all PTMs or a string denoting a specfic PTM type (as written in input peptide lists), or 'pathway'. If plot_type = 'ptm', residue can equal any string of single-letter amino acids to plot only PTMs on those residues (E.g. residue = 'NQR').
  • Protein fold change VS PTM fold change plot can be made with:

::

new_instance.proteinVSptm(ptm_type,          # String deonting PTM type to graph (as written in peptide list input files).
                         residue = 'any',    # String containing single-letter amino acid denoting which residues to plot.
                         exp = 1,            # Index for numerator in fold change calculation. Defaults to 1 (i.e. second column).
                         ctrl = 0,           # Index for denominator in fold change calculation. Defaults to 0 (i.e. first column). Ignored if continuous = True.
                         continuous = False  # Bool denoting whether variable in column indicated by exp is continuous. 
                         )

5. Contrasts and significance testing

Significance testing comparing all treatments to a single control group can be performed using new_instance.doContrasts() as follows:

::

new_instance.doContrasts(Contrasted,      # String denoting which contrasts to test. Can be either 'protein', 'ptm', 'other' or 'pathway'. Defaults to 'protein'.
                         ctrl,            # Int denoting which column to use as the control group. Defaults to 0, meaning the first column. Ignored if continuous = True.
                         propagateErrors, # Bool deonting whether to propagate control group errors into experimental group errors (using square root of sum of squares) for t-statistic calculation (Welch's t-test). Defualts to False.
                         UseBayesFactors,  # Bool denoting whether to use Bayes Factors rather than p-values. Still needs testing. Defaults to False.
                         continuous        # Bool denoting whether variable to be contrasted is continuous and test should be only to see if it is significantly different from zero.
                         )

This will add the Contrasted dataframe property to new_instance that can be inspected and manipulated by new_instance.Contrasted.

6. Load previous analysis

A previous BayesENproteomics instance (we'll stick with our example, new_instance) can be loaded using new_instance.load(), provided that new_instance is defined as in step 1. new_instance.load() will look for the folder created during step 1 (named using the output_name arguement). If this folder cannot be found, an error will be raised.