What is it about?
Deletion of glutamate racemase (murI) in M. smegmatis is initially bacteriostatic, but following prolonged incubation, a revertant phenotype consistently develops, which is due to overexpression of MSMEG_5795. This gene is currently annotated as 4-amino-4-deoxychorismate lyase, but in this study, it is found to have D-amino acid transaminase activity. The MSMEG_5795 gene, with overexpression, is able to rescue deletion mutants of either glutamate racemase or alanine racemase and could play an important role in mycobacterial cell wall metabolism, and should be reannotated as a D-amino acid transaminase.
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Why is it important?
Glutamate racemase is an essential enzyme in mycobacteria and thus a target for drug discovery. Finding an enzyme that, when over-expressed, can compensate for the loss of glutamate racemase (MurI) could have implications with respect to research that hopes to target tuberculosis through the inhibition of MurI.
Perspectives
The essentiality of glutamate racemase in mycobacteria has been a puzzle through the years with some studies finding that it was, and others that it wasn't essential. More recent work has solidly come done on the side of MurI being essential. Some earlier research pointed to the possibility that there might be a D-amino acid transaminase in mycobacteria, but it had not been identified. It is tempting to speculate that the activity of this misannotated enzyme, MSMEG_5795 could be behind the conflicting results.
Kurt Krause
University of Otago
Read the Original
This page is a summary of: Overexpression of a newly identified d-amino acid transaminase in Mycobacterium smegmatis
complements glutamate racemase deletion, Molecular Microbiology, December 2017, Wiley,
DOI: 10.1111/mmi.13877.
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