Distinct specificities of the HEMK2 protein methyltransferase in methylation of glutamine and lysine residues

Abstract

The HEMK2 protein methyltransferase has been described as glutamine methyltransferase catalyzing ERF1‐Q185me1 and lysine methyltransferase catalyzing H4K12me1. Methylation of two distinct target residues is unique for this class of enzymes. To understand the specific catalytic adaptations of HEMK2 allowing it to master this chemically challenging task, we conducted a detailed investigation of the substrate sequence specificities of HEMK2 for Q‐ and K‐methylation. Our data show that HEMK2 prefers methylation of Q over K at peptide and protein level. Moreover, the ERF1 sequence is strongly preferred as substrate over the H4K12 sequence. With peptide SPOT array methylation experiments, we show that Q‐methylation preferentially occurs in a G‐Q‐X3‐R context, while K‐methylation prefers S/T at the first position of the motif. Based on this, we identified novel HEMK2 K‐methylation peptide substrates with sequences taken from human proteins which are methylated with high activity. Since H4K12 methylation by HEMK2 was very low, other protein lysine methyltransferases were examined for their ability to methylate the H4K12 site. We show that SETD6 has a high H4K12me1 methylation activity (about 1000‐times stronger than HEMK2) and this enzyme is mainly responsible for H4K12me1 in DU145 prostate cancer cells.

Cytosolic N6AMT1-dependent translation supports mitochondrial RNA processing

“…Interestingly, N6AMT1 orthologs in bacteria and yeast are also involved in translation, and while we report that the molecular function of N6AMT1 in humans has diverged, as it does not involve ribosome assembly or translation termination (Figure 2A, B), our results nevertheless indicate that N6AMT1 has retained a canonical role in protein synthesis that appears to depend on its catalytic activity (Figure 3C). Previous work identified translation-related factors, such as RRP1, EIF2BD, and eRF1 22,25,45,46 , as substrates for N6AMT1, while in yeast, Mtq2 interacts with ribosomal proteins 24 . Further work will be necessary to clarify which of the potential N6AMT1 methylation targets accounts for its role in translation regulation.…”