Precise characterization of KRAS4b proteoforms in human colorectal cells and tumors reveals mutation/modification cross-talk

Significance The KRAS gene is frequently mutated in human cancer, especially in pancreatic, lung, and colorectal tumors. We developed an intact protein assay for the detection and quantitation of KRAS protein forms (proteoforms), enabling the measurement of how genetically encoded mutations affect posttranslational modifications on the same protein molecule. The modifications found are known to activate KRAS or interfere with membrane attachment, suggesting cellular mechanisms that control downstream KRAS activity. Analysis of wild-type and mutant-specific forms of the KRAS protein with complete molecular specificity is shown to be possible by top-down proteomics and enables future tests of how an individual’s KRAS proteoforms are linked to disease stage and chance of survival.