Abstract of the PDB Structure's related Publication:
BCDIN3 domain containing RNA methyltransferase, BCDIN3D, monomethylates the 5'-monophosphate of cytoplasmic tRNAHis with a G-1:A73 mispair at the top of an eight-nucleotide-long acceptor helix, using S-adenosyl-l-methionine (SAM) as a methyl group donor. In humans, BCDIN3D overexpression is associated with the tumorigenic phenotype and poor prognosis in breast cancer. Here, we present the crystal structure of human BCDIN3D complexed with S-adenosyl-l-homocysteine. BCDIN3D adopts a classical Rossmann-fold methyltransferase structure. A comparison of the structure with that of the closely related methylphosphate capping enzyme, MePCE, which monomethylates the 5'-γ-phosphate of 7SK RNA, revealed the important residues for monomethyl transfer from SAM onto the 5'-monophosphate of tRNAHis and for tRNAHis recognition by BCDIN3D. A structural model of tRNAHis docking onto BCDIN3D suggested the molecular mechanism underlying the different activities between BCDIN3D and MePCE. A loop in BCDIN3D is shorter, as compared to the corresponding region that forms an α-helix to recognize the 5'-end of RNA in MePCE, and the G-1:A73 mispair in tRNAHis allows the N-terminal α-helix of BCDIN3D to wedge the G-1:A73 mispair of tRNAHis. As a result, the 5'-monophosphate of G-1 of tRNAHis is deep in the catalytic pocket for 5'-phosphate methylation. Thus, BCDIN3D is a tRNAHis-specific 5'-monomethylphosphate capping enzyme that discriminates tRNAHis from other tRNA species, and the structural information presented in this study also provides the molecular basis for the development of drugs against breast cancers.
Bicoid Interacting 3-domain containing RNA methyltransferases is a member of the Bin 3 methyltransferase enzyme family, a from worm-to-human evolutionarily conserved protein family (Liu et al. 2020 ). From a structural point of view, it possesses an S-adenosyl-dependent-methyltransferases (SMA) domain that, as in its closely related human orthologue BCDIN3, is used as a methyl group trasfer.
It indeed recognizes the acceptor helix of tRNAHis with a G-1 A73 mispair at the top of the eight-nucleotide long acceptor helix and the G-1 nucleobase. There is some controversy about the methylation of pre-miR 145 since the demethylation described precedently could not be reproduced in some more recent work (Xhemalce et al. 2012 )