Identification of a Tumor Specific， Active-Site Mutation in Casein Kinase 1α by Chemical Proteomics.

We describe the identification of a novel， tumor-specific missense mutation in the active site of casein kinase 1α (CSNK1A1) using activity-based proteomics. Matched normal and tumor colon samples were analyzed using an ATP acyl phosphate probe in a kinase-targeted LC-MS2 platform. An anomaly in the active-site peptide from CSNK1A1 was observed in a tumor sample that was consistent with an altered catalytic aspartic acid. Expression and analysis of the suspected mutant verified the presence of asparagine in the probe-labeled， active-site peptide for CSNK1A1. Genomic sequencing of the colon tumor samples confirmed the presence of a missense mutation in the catalytic aspartic acid of CSNK1A1 (GAC→AAC). To our knowledge， the D163N mutation in CSNK1A1 is a newly defined mutation to the conserved， catalytic aspartic acid of a protein kinase and the first missense mutation identified using activity-based proteomics. The tumorigenic potential of this mutation remains to be determined.