trmI

TrmI, or tRNA (guanine(10)-N2)-methyltransferase, is a tRNA-modifying enzyme found in many bacteria and some archaea. It catalyzes the S-adenosyl-L-methionine (SAM)-dependent methylation of guanine at position 10 in transfer RNA, producing N2-methylguanosine at position 10 (m2G10) and S-adenosylhomocysteine as a byproduct.

Genes and distribution: The enzyme is encoded by the trmI gene and participates in tRNA modification pathways. It is common in several thermophilic bacteria and some archaeal species, though not universal across all taxa. Its presence often correlates with organisms that rely on robust tRNA stability under high temperatures.

Structure and mechanism: TrmI typically forms a homotetramer, with each subunit contributing to a catalytic pocket at subunit interfaces. It belongs to the family of SAM-dependent methyltransferases that adopt a Rossmann-like fold. The catalytic process involves transfer of the methyl group from SAM to the exocyclic amino nitrogen (N2) of G10 in the tRNA, a mechanism consistent with many class I methyltransferases and supported by structural studies of TrmI homologs.

Substrate specificity and function: The enzyme shows specificity for tRNA molecules bearing guanine at position 10. Methylation at G10 is thought to influence tRNA folding and stability, which can affect translation efficiency and accuracy, particularly in organisms exposed to thermal stress where such modifications are beneficial.

Discovery and model systems: TrmI has been studied in thermophilic bacteria such as Thermus thermophilus and Thermotoga maritima, where biochemical and structural analyses have illuminated its tetrameric architecture and active-site features, contributing to a broader understanding of tRNA modification enzymes.