METTL21C methylates Alanine tRNA synthetase at lysine 943 in muscle tissue

ABSTRACT: Protein lysine methylation is a common post-translational modification (PTM) detected throughout the human proteome that plays important roles in diverse biological processes. In the human genome, there are greater than one hundred known and candidate protein lysine methyltransferases (PKMTs), many with important links to human disease. METTL21C (methyltransferase-like protein 21C) is a PKMT implicated in muscle biology and reported to methylate VCP (valosin-containing protein/p97) and HSPA8 (heat shock 70kDa protein 8). However, a clear in vitro methyltransferase activity for METTL21C is yet to be demonstrated. Thus, whether METTL21C is indeed an active enzyme that directly methylates substrate/s is unclear. Here, we use an unbiased biochemical-based screening assay coupled to mass spectrometry to identify Alanine-tRNA-Synthetase 1 (AARS1) as a direct substrate of METTL21C. METTL21C catalyzes mono-, di- and tri-methylation of lysine 943 of AARS1 (AARS1-K943me) in vitro and in vivo. In vitro methylation of AARS1 by METTL21C is independent of ATP or tRNA molecules. In contrast to AARS1, and in conflict with previous reports, we do not detect METTL21C methylation activity on VCP and HSPA8. Depletion of METTL21C in METTL21C-expressing cells leads to depletion of AARS1-K943 methylation. Finally, METTL2C is almost exclusively expressed in muscle tissue, and accordingly we detect the METTL21C-catalyzed methylation event of AARS1 in mouse skeletal muscle tissue. Together, our work identifies AARS1 as a bona fide substrate of METTL21C and suggests a role for the METTL21C-AARS1 axis in the regulation of protein synthesis in muscle tissue. In addition, our study describes a straightforward protocol for elucidating physiologic substrates of little characterized or uncharacterized PKMTs

INSTRUMENT(S): Orbitrap Fusion

ORGANISM(S): Homo Sapiens (human)

SUBMITTER: Mohamad Zoabi  

LAB HEAD: Or Gozani

PROVIDER: PXD019886 | Pride | 2020-07-02

REPOSITORIES: Pride