Aminotransferase activity of a novel aminoacyl‐tRNA synthetase appended domain (751.3)

Aminoacyl‐tRNA synthetases (AARSs) are key enzymes in protein biosynthesis, responsible for attaching amino acids to the 3ʹ‐end of cognate tRNAs. The AARSs are modular proteins, with separate polypeptide domains responsible for tRNA binding and catalysis; additional domains on some AARSs contribute oligomerization, localization, and editing functions. The opportunistic pathogen Mycoplasms penetrans expresses an unusually long version of methionyl‐tRNA synthetase (MetRS) that contains an extra N‐terminal domain with sequence homology to class V aminotransferases. We anticipated that this domain carries out pyridoxal phosphate (PLP)‐dependent aminotransferase activity, possibly to modify Met‐tRNA(Met) for enhanced pathogenicity. We overexpressed and purified M. penetrans MetRS (MpMetRS) and used the amino‐reactive aromatic dialdehyde naphthalene‐2,3‐dicarboxaldehyde followed by HPLC to analyze enzyme activity in vitro. Initial characterization confirms the proposed aminotransferase activity, with several amino acids and α‐keto acids serving as amino group donors and acceptors, respectively. Substitution of amino acids in the transferase and synthetase catalytic sites indicate that these activities are independent. Ultimately we seek to identify the cellular substrates and implications of the MpMetRS aminotransferase activity. Grant Funding Source : Supported by the National Science Foundation