Crystal structure of tRNA(m1G37)methyltransferase: insights into tRNA recognition

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Oxford University Press

RESUMO

tRNA(m1G37)methyltransferase (TrmD) catalyzes the transfer of a methyl group from S-adenosyl-l- methionine (AdoMet) to G37 within a subset of bacterial tRNA species, which have a G residue at the 36th position. The modified guanosine is adjacent to and 3′ of the anticodon and is essential for the maintenance of the correct reading frame during translation. Here we report four crystal structures of TrmD from Haemophilus influenzae, as binary complexes with either AdoMet or S-adenosyl-l-homocysteine (AdoHcy), as a ternary complex with AdoHcy and phosphate, and as an apo form. This first structure of TrmD indicates that it functions as a dimer. It also suggests the binding mode of G36G37 in the active site of TrmD and the catalytic mechanism. The N-terminal domain has a trefoil knot, in which AdoMet or AdoHcy is bound in a novel, bent conformation. The C-terminal domain shows structural similarity to trp repressor. We propose a plausible model for the TrmD2–tRNA2 complex, which provides insights into recognition of the general tRNA structure by TrmD.

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