The crystal structure of Escherichia coli methionyl-tRNAfMet transformylase
complexed with formyl-methionyl-tRNAfMet was solved at 2.8 A resolution. The
formylation reaction catalyzed by this enzyme irreversibly commits
methionyl-tRNAfMet to initiation of translation in eubacteria. In the
three-dimensional model, the methionyl-tRNAfMet formyltransferase fills in the
inside of the L-shaped tRNA molecule on the D-stem side. The anticodon stem and
loop are away from the protein. An enzyme loop is wedged in the major groove of
the acceptor helix. As a result, the C1-A72 mismatch characteristic of the
initiator tRNA is split and the 3' arm bends inside the active centre. This
recognition mechanism is markedly distinct from that of elongation factor Tu,
which binds the acceptor arm of aminoacylated elongator tRNAs on the T-stem side.
