Fig. 3.

KRAS4b proteoform detection in tumor samples. (A) MS1 data for the 23+ charge state of KRAS4b detected from a tumor carrying the G13D mutation (Upper) and a tumor containing no KRAS mutations (Lower). Fully processed KRAS4b is highlighted in red, and KRAS4b lacking the COOMe is highlighted in orange. Asterisks denote known ESI oxidation products. (B) Zoomed-in fragmentation spectrum illustrating detection of the b₅₃ ion from two sequence variants, WT (red) and G13D (cyan). Intensities of these ions were used to calculate relative abundances of mutant and WT KRAS in Table 2. (C) Zoomed-in fragmentation spectrum illustrating detection of the y₁₂ ion from KRAS4b proteoforms with and without the C-terminal methyl ester, KRAS4b-FMe (red) and KRAS4b-Farn (orange), respectively. Intensities of these ions were used to calculate percentage of C-terminal COOMe in Table 2.