Identification, Quantification and Systems Analysis of Protein N-ε Lysine Methylation in Anucleate Blood Platelets.

Protein post-translational modifications critically regulate a range of physiological and disease processes. In addition to tyrosine, serine and threonine phosphorylation, reversible N-ε acylation and alkylation of protein lysine residues also modulate diverse aspects of cellular function. Studies of lysine acyl and alkyl modifications have focused on nuclear proteins in epigenetic regulation; however, lysine modifications are also prevalent on cytosolic proteins to serve increasingly apparent, although less understood roles in cell regulation. Here, we characterize the methyl-lysine (meK) proteome of anucleate blood platelets. With high-resolution, multiplex mass spectrometry methods, we identify 190 mono-, di- and tri-meK modifications on 150 different platelet proteins - including 28 meK modifications quantified by tandem mass tag (TMT) labeling. In addition to identifying meK modifications on calmodulin (CaM), GRP78 (HSPA5, BiP) and EF1A1 that have been previously characterized in other cell types, we also uncover more novel modifications on cofilin, drebin-like protein (DBNL, Hip-55), DOCK8, TRIM25 and numerous other cytoplasmic proteins. Together, our results and analyses support roles for lysine methylation in mediating cytoskeletal, translational, secretory and other cellular processes. Mass spectrometry data for this study have been deposited into the ProteomeXchange Consortium via the PRIDE partner repository with the dataset identifier PXD012217. This article is protected by copyright. All rights reserved.