InterPro domain: IPR033671

tRNA (guanosine(18)-2'-O)-methyltransferase (also known as tRNA [Gm18] methyltransferase, and TrmH) catalyses the 2'-O methylation of guanosine at position 18 (Gua18) in the D loop of tRNA [ 1 ]. In the reaction, S-adenosyl-L-methionine (AdoMet) functions as a methyl group donor and is converted to S-adenosyl-L-homocysteine (AdoHcy). The methylation of tRNA nucleotides helps to stabilize the L-shaped tRNA structure and improve their molecular recognition [ 2 ].

TrmH enzymes can be classified into two types based on their substrate tRNA specificity. Type I TrmH, which includes Thermus thermophilus TrmH, can modify all tRNA species. Type II TrmH, which includes Echerichia coli TrmH and Saccharomyces cerevisiae TrmH, modifies only a subset of tRNA species [ 3 ].

1. Deep knot structure for construction of active site and cofactor binding site of tRNA modification enzyme. Structure 12, 593-602
2. The catalytic domain of topological knot tRNA methyltransferase (TrmH) discriminates between substrate tRNA and nonsubstrate tRNA via an induced-fit process. J. Biol. Chem. 288, 25562-74
3. Aquifex aeolicus tRNA (Gm18) methyltransferase has unique substrate specificity. TRNA recognition mechanism of the enzyme. J. Biol. Chem. 278, 25081-90