METTL21B is a novel human lysine methyltransferase of translation elongation factor 1A: discovery by CRISPR/Cas9 knock out

ABSTRACT: Lysine methylation is widespread on human proteins, however the enzymes that catalyse its addition remain largely unknown. This limits our capacity to study the function and regulation of this modification. Here we report that human METTL21B is a protein methyltransferase, which methylates lysine 165 of eukaryotic translation elongation factor 1A (eEF1A). The CRISPR/Cas9 system was used to knock out putative protein methyltransferases METTL21B and METTL23 in K562 cells. The known eEF1A methyltransferase EEF1AKMT1 was also knocked out as a control. Targeted mass spectrometry revealed the loss of lysine 165 methylation upon knock out of METTL21B, and the expected loss of lysine 79 methylation on knock out of EEF1AKMT1. No loss of eEF1A methylation was seen in the METTL23 knock out. Recombinant METTL21B was then shown to catalyse methylation on lysine 165 in eEF1A1 and eEF1A2 in vitro, confirming it as the methyltransferase responsible for this methylation site. Stable isotope labelling by amino acids in cell culture (SILAC) proteomic analysis revealed dysregulation of processes related to eEF1A function in knock outs of METTL21B and EEF1AKMT1, but specific dysregulation of ribosomal proteins in the knock out of METTL21B. This indicates a specific function for lysine 165 methylation of eEF1A in human. METTL21B is specific to vertebrates, with its target lysine showing similar evolutionary conservation. We suggest METTL21B be renamed eEF1A-KMT3. This is the first study to specifically generate CRISPR/Cas9 knock outs of the genes encoding putative protein methyltransferases, for the purpose of substrate discovery and site mapping. Our approach should prove useful for the discovery of further novel methyltransferases, and more generally for the discovery of sites for other protein-modifying enzymes.

INSTRUMENT(S): Q Exactive

ORGANISM(S): Homo Sapiens (human)

SUBMITTER: Joshua Hamey  

LAB HEAD: Marc R Wilkins

PROVIDER: PXD005497 | Pride | 2017-07-03

REPOSITORIES: Pride