Structural basis of arginine asymmetrical dimethylation by PRMT6.

PRMT6 is a type I protein arginine methyltransferase, generating the asymmetric dimethylarginine mark on proteins such as histone H3R2. Asymmetric dimethylation of histone H3R2 by PRMT6 acts as a repressive mark that antagonizes trimethylation of H3 lysine 4 by the MLL histone H3K4 methyltransferase. PRMT6 is overexpressed in several cancer types, including prostate, bladder and lung cancers; therefore, it is of great interest to develop potent and selective inhibitors for PRMT6. Here we report the synthesis of a potent bi-substrate inhibitor GMS (6′-methyleneamine sinefungin, an analogue of sinefungin), and the crystal structures of human PRMT6 in complex respectively with SAH and the bi-substrate inhibitor GMS that shed light on the significantly improved inhibition effect of GMS on methylation activity of PRMT6 compared to SAH and a SAM competitive methyltransferase inhibitor sinefungin (SNF). In addition, we also crystallized PRMT6 in complex with SAH and a short arginine containing peptide. Based on the structural information here and available in the PDB database, we propose a mechanism that can rationalize the distinctive arginine methylation product specificity of different types of arginine methyltransferases and pinpoint the structural determinant of such a specificity.