Overexpression of a newly identified d-amino acid transaminase in Mycobacterium smegmatis complements glutamate racemase deletion

Mol Microbiol. 2018 Jan;107(2):198-213. doi: 10.1111/mmi.13877. Epub 2017 Dec 7.


Glutamate racemase (MurI) has been proposed as a target for anti-tuberculosis drug development based on the inability of ΔmurI mutants of Mycobacterium smegmatis to grow in the absence of d-glutamate. In this communication, we identify ΔmurI suppressor mutants that are detected during prolonged incubation. Whole genome sequencing of these ΔmurI suppressor mutants identified the presence of a SNP, located in the promoter region of MSMEG_5795. RT-qPCR and transcriptional fusion analyses revealed that the ΔmurI suppressor mutant overexpressed MSMEG_5795 14-fold compared to the isogenic wild-type. MSMEG_5795, which is annotated as 4-amino-4-deoxychorismate lyase (ADCL) but which also has homology to d-amino acid transaminase (d-AAT), was expressed, purified and found to have d-AAT activity and to be capable of producing d-glutamate from d-alanine. Consistent with its d-amino acid transaminase function, overexpressed MSMEG_5795 is able to complement both ΔmurI deletion mutants and alanine racemase (Δalr) deletion mutants, thus confirming a multifunctional role for this enzyme in M. smegmatis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alanine / metabolism
  • Alanine Racemase / genetics
  • Alanine Racemase / metabolism
  • Amino Acid Isomerases / genetics
  • Amino Acid Isomerases / metabolism*
  • Base Sequence / genetics
  • D-Alanine Transaminase / chemistry
  • D-Alanine Transaminase / genetics
  • D-Alanine Transaminase / metabolism*
  • Gene Deletion
  • Glutamic Acid / metabolism
  • Mycobacterium smegmatis / enzymology*
  • Mycobacterium smegmatis / genetics
  • Oxo-Acid-Lyases / chemistry
  • Oxo-Acid-Lyases / genetics
  • Oxo-Acid-Lyases / metabolism*
  • Promoter Regions, Genetic
  • Suppression, Genetic
  • Whole Genome Sequencing


  • Glutamic Acid
  • D-Alanine Transaminase
  • Oxo-Acid-Lyases
  • aminodeoxychorismate lyase
  • Amino Acid Isomerases
  • Alanine Racemase
  • glutamate racemase
  • Alanine