mnmG

MnmG, also known as GidA (glucose-inhibited division A), is a bacterial enzyme that participates in the modification of uridine at the wobble position U34 of several tRNAs. It is a key component of the MnmE–MnmG (TrmE–GidA) system that coordinates tRNA base modifications required for efficient and accurate decoding of codons for certain amino acids, notably lysine, glutamate, and glutamine.

Biochemically, MnmG is a flavin adenine dinucleotide (FAD)-dependent oxidoreductase that forms a complex with MnmE, a GTPase. The MnmE–MnmG complex catalyzes the installation of a carboxymethylaminomethyl (cmnm) group at U34, yielding cmnm5s2U. In many organisms, a subsequent action by MnmC converts cmnm5s2U to mnm5s2U, completing the modification pathway. GTP hydrolysis by MnmE and the FAD-dependent chemistry of MnmG drive the reaction, linking tRNA modification to energy and redox state.

Biological significance is tied to translational fidelity and efficiency. Proper U34 modifications improve decoding accuracy and load, while defects in MnmG or disruption of the MnmE–MnmG system can cause slower growth, temperature sensitivity, increased miscoding, and altered responses to environmental stresses or antibiotics in some bacteria.

Distribution and structure-wise, MnmG is highly conserved in bacteria and typically comprises around several hundred amino acids, forming a dimeric FAD-dependent protein that interacts with MnmE. The gidA/mnmG designation reflects its discovery via the glucose-inhibited division phenotype and its later identification as a tRNA-modifying enzyme.