ProteoForge: An Imputation-Aware Framework for Differential Proteoform Discovery in Bottom-Up Proteomics

The human genome contains approximately 20,000 protein-coding genes. However, millions of diverse protein variants, called proteoforms, exist. Despite originating from the same gene, proteoforms often have distinct biological roles. In bottom-up proteomics, the aggregation of peptide measurements into protein-level quantities often obscures this information. Existing methods for differential proteoform discovery are limited by their handling of missing data, which can introduce a significant bias. To address this, we developed ProteoForge, which builds on an imputation-aware statistical model to identify and group covarying peptides into quantitatively differential proteoforms (dPFs). Benchmarking against existing methods demonstrated that ProteoForge provides high accuracy and stability in data sets with high rates of missing values, complex experimental designs, or varying signal strengths. Application of ProteoForge to proteomics data from lung cancer cells under hypoxia revealed extensive proteoform-level regulation hidden by a standard protein-level analysis.