Cited by 68Advanced Proteomics Techniques and ApplicationsMass Spectrometry Techniques and ApplicationsAdvanced Biosensing Techniques and Applications

Covariation of Peptide Abundances Accurately Reflects Protein Concentration Differences

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Zhang, Bo, Pirmoradian, Mohammad, Zubarev, Roman, Käll, Lukas·2017·Molecular & Cellular Proteomics

Abstract

Most implementations of mass spectrometry-based proteomics involve enzymatic digestion of proteins, expanding the analysis to multiple proteolytic peptides for each protein. Currently, there is no consensus of how to summarize peptides' abundances to protein concentrations, and such efforts are complicated by the fact that error control normally is applied to the identification process, and do not directly control errors linking peptide abundance measures to protein concentration. Peptides resulting from suboptimal digestion or being partially modified are not representative of the protein concentration. Without a mechanism to remove such unrepresentative peptides, their abundance adversely impacts the estimation of their protein's concentration. Here, we present a relative quantification approach, Diffacto, that applies factor analysis to extract the covariation of peptides' abundances. The method enables a weighted geometrical average summarization and automatic elimination of incoherent peptides. We demonstrate, based on a set of controlled label-free experiments using standard mixtures of proteins, that the covariation structure extracted by the factor analysis accurately reflects protein concentrations. In the 1% peptide-spectrum match-level FDR data set, as many as 11% of the peptides have abundance differences incoherent with the other peptides attributed to the same protein. If not controlled, such contradicting peptide abundance have a severe impact on protein quantifications. When adding the quantities of each protein's three most abundant peptides, we note as many as 14% of the proteins being estimated as having a negative correlation with their actual concentration differences between samples. Diffacto reduced the amount of such obviously incorrectly quantified proteins to 1.6%. Furthermore, by analyzing clinical data sets from two breast cancer studies, our method revealed the persistent proteomic signatures linked to three subtypes of breast cancer. We conclude that Diffacto can facilitate the interpretation and enhance the utility of most types of proteomics data.

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  • Several proposed methods exclude peptide measurements from the aggregate protein quantity when they are outliers relative to other peptides mapping to the same protein-coding gene.

    “The approach of several proposed methods focuses on the exclusion of peptide measurements from inclusion in the aggregate protein quantity if they are outliers from other peptide measurements mapping to the same protein coding gene.(28–33)”
  • Outlier-exclusion methods improve protein concentration estimates but still report only one protein quantity and ignore peptides that do not agree with that value.

    “While these all demonstrate improved protein concentration estimates, they still only report a single protein quantity and ignore peptides that do not agree with that single value.”

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Authors
Zhang, B., Pirmoradian, M., Zubarev, R., & Käll, L.
Affiliations
  • Karolinska Institutet (SE)
  • Karolinska University Hospital (SE)
  • Science for Life Laboratory (SE)
Corresponding author
  • Zubarev, Roman
  • Käll, Lukas
Venue
Molecular & Cellular Proteomics
Publisher
Elsevier BV
Published
2017-05
Volume
16
Issue
5
Pages
936-948
ISSN
1535-9476 (ISSN-L)
OpenAlex
W2596516271
Cited by
68
References
63
Citations by year
2026: 3 · 2025: 7 · 2024: 3 · 2023: 11 · 2022: 9 · 2021: 8 · 2020: 8 · 2019: 8 · 2018: 9 · 2017: 2
FWCI
3.64
Type
journal article
Language
en
Open access
Locations
  • Molecular & Cellular Proteomics (publishedVersion, cc-by)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
Funders
Knut och Alice Wallenbergs Stiftelse (2010.0022)
Topics
  • Physical Sciences › Chemistry › Spectroscopy › Advanced Proteomics Techniques and Applications
  • Physical Sciences › Chemistry › Spectroscopy › Mass Spectrometry Techniques and Applications
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Advanced Biosensing Techniques and Applications
Keywords
factor analysis, label-free quantification, peptide-spectrum matches, false discovery rate, breast cancer subtypes
MeSH terms
Breast Neoplasms, Female, Humans, Peptides, Proteins, Saccharomyces cerevisiae, Software, Sequence Analysis, Protein, Proteomics, Signal-To-Noise Ratio

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