Homogeneous recombinant Mycobacterium tuberculosis shikimate dehydrogenase production: An essential step towards target-based drug design

BackgroundThe shikimate pathway is an attractive target for the development of antitubercular agents because it is essential in Mycobacterium tuberculosis, the causative agent of tuberculosis, but absent in humans. M. tuberculosis aroE-encoded shikimate dehydrogenase catalyzes the forth reaction in the shikimate pathway. Structural and functional studies indicate that Lysine69 may be involved in catalysis and/or substrate binding in M. tuberculosis shikimate dehydrogenase. Investigation of the kinetic properties of mutant enzymes can bring important insights about the role of amino acid residues for M. tuberculosis shikimate dehydrogenase.FindingsWe have performed site-directed mutagenesis, steady-state kinetics, equilibrium binding measurements and molecular modeling for both the wild-type M. tuberculosis shikimate dehydrogenase and the K69A mutant enzymes. The apparent steady-state kinetic parameters for the M. tuberculosis shikimate dehydrogenase were determined; the catalytic constant value for the wild-type enzyme (50 s-1) is 68-fold larger than that for the mutant K69A (0.73 s-1). There was a modest increase in the Michaelis-Menten constant for DHS (K69A = 76 μM; wild-type = 29 μM) and NADPH (K69A = 30 μM; wild-type = 11 μM). The equilibrium dissociation constants for wild-type and K69A mutant enzymes are 32 (± 4) μM and 134 (± 21), respectively.ConclusionOur results show that the residue Lysine69 plays a catalytic role and is not involved in substrate binding for the M. tuberculosis shikimate dehydrogenase. These efforts on M. tuberculosis shikimate dehydrogenase catalytic mechanism determination should help the rational design of specific inhibitors, aiming at the development of antitubercular drugs.

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“…The recombinant Mtb SD protein purification protocol resulted in a protein yield of 13%, according to the previous protocol [12]. …”

Section: Findings and Discussionmentioning

confidence: 99%

“…The freeze-thaw method was used to release the proteins in the soluble fraction [8]. The purification protocol was as previously described [12]. Samples of the purification steps were analyzed by SDS-PAGE [13] and protein content by the Bradford's method [14].…”

Section: Methodsmentioning

confidence: 99%