Histidine methylation of MYLK2 and C3H zinc fingers by CARNMT1

We here describe our independent uncovering of CARNMT1 as a protein histidine methyltransferase (HMT), and our extensive efforts on defining its substrate specificity and methylation targets. We found that recombinant CARNMT1 methylated MYLK2-derived peptide containing His-148 in vitro. The recombinant CARNMT1 methylated also several proteins in extracts from CARNMT1 KO cells, and, using protein mass spectrometry, we identified several fully methylated CARNMT1 targets, all of which were C3H zinc finger (C3H ZnF) proteins. These included the previously identified U2AF1, ZC3H15 and ZC3H18, but also the novel substrates RBM22, PPP1R10, PRR3 and RNF113A. We also identified several of the homologous methylation events in Caenorhabditis elegans and showed that they could be introduced by the nematode CARNMT in vitro.