Deletion of a mycobacterial gene encoding a reductase leads to an altered cell wall containing β-oxo-mycolic acid analogues, and the accumulation of long-chain ketones related to mycolic acids

same study, the authors also used bioinformatics to identify Rv2509, the M. tuberculosis
ortholog of NCgl2385, as a possible candidate for reduction of the mycolic acid motif (Lea-
Smith et al., 2007). Mycobacterium smegmatis has often been used as a surrogate for M.
tuberculosis when studying biosynthetic pathways. The fast growing, non-pathogenic M.
smegmatis strain is particularly useful in studying cell wall biosynthesis genes since it can
tolerate deletion of some genes that are essential in M. tuberculosis (Amin et al., 2008; Escuyer
et al., 2001). Moreover, while the two species differ in mero-chain modifications, core enzymes
involved in mycolate biosynthesis are interchangeable (Brown et al., 2007; Parish et al., 2007).
We thus chose to address the role of Rv2509 in mycobacterial mycolic acid biosynthesis by
generating a deletion mutant of MSMEG4722, the M. smegmatis homologue of Rv2509.

RESULTS

MSMEG4722 and Rv2509 encode proteins structurally similar to short chain
reductases/dehydrogenases

Using bioinformatics, Lea-Smith et al. (2007) identified M. tuberculosis Rv2509 as the
homologue of NCgl2385, the C. glutamicum reductase involved in mycolic acid motif formation.
The closest match for Rv2509 in the M. smegmatis mc²155 genome was the putative protein
MSMEG4722 (Figure 1B). Both predicted proteins contained conserved active site residues and
residues for NAD/NADP binding (Figure 1B). Predictions of the three-dimensional structures of
proteins often give insights into potential catalytic properties. We used the @TOME server to
screen for known structures of proteins that were predicted to be most closely related to Rv2509
(Douguet and Labesse, 2001). Predictions of E-values from TITO and 3D-PSSM servers (-

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