Mycobacterium tuberculosis methionyl-tRNA synthetase (MetRS) has been cloned and characterized. The protein contains class I signature sequences but lacks the Zn2+ binding motif and the C-terminal dimerization appendix that are found in MetRSs from several organisms including E. coli MetRS. Consistent with these features, the enzyme behaved as a monomer in a gel filtration chromatography and did not contain the bound Zn2+. Nonetheless, it was active to the tRNA(Met) of E. coli as determined by in vivo genetic complementation and in vitro reaction. Phylogenetic analysis separated the M. tuberculosis and E. coli MetRSs into prokaryote and eukaryote-archaea group, respectively. This result is consistent with the taxonomic locations of the organism but is an interesting contrast to the case of its paralogous protein, isoleucyl-tRNA synthetase, and suggests that the two enzymes evolved in separate idiosyncratic pathways.
Bibliographical noteFunding Information:
We thank Drs. P. Schimmel for providing insight, S. Nair for M. kansasii genomic DNA, R. Young for a λgt11 M. tuberculosis library, and K.C. Lee for the HPLC experiment. This work was supported in part by a National Institutes of Health SBIR Grant #1R431I36615-01A1 to S.A.M. (USA), a grant from the Ministry of Education, Science, and Culture (Japan) and by BSRI-96-4417 and HMP-96-D-1-0016 (Korea).
All Science Journal Classification (ASJC) codes
- Structural Biology
- Molecular Biology
- Cell Biology