Abstract
Backgroundα-isopropylmalate synthase (MtαIPMS), an enzyme that catalyzes the first committed step of the leucine biosynthetic pathway of Mycobacterium tuberculosis is a potential drug target for the anti-tuberculosis drugs. Cations induce differential effect of activation and inhibition of MtαIPMS. To date no concrete mechanism for such an opposite effect of similarly charged cations on the functional activity of enzyme has been presented.ResultsEffect of cations on the structure and function of the MtαIPMS has been studied in detail. The studies for the first time demonstrate that different cations interact specifically at different sites in the enzyme and modulate the enzyme structure differentially. The inhibitors Zn2+ and Cd2+ ions interact directly with the catalytic domain of the enzyme and induce unfolding/denaturation of the domain. The activator K+ also interacts with the catalytic TIM barrel domain however, it does not induce any significant effect on the enzyme structure. Studies with isolated catalytic TIM barrel domain showed that it can carry out the catalytic function on its own but probably requires the non-catalytic C-terminal domain for optimum functioning. An important observation was that divalent cations induce significant interaction between the regulatory and the catalytic domain of MtαIPMS thus inducing structural cooperativity in the enzyme. This divalent cation induced structural cooperativity might result in modulation of activity of the catalytic domain by regulatory domain.ConclusionThe studies for the first time demonstrate that different cations bind at different sites in the enzyme leading to their differential effects on the structure and functional activity of the enzyme.
Highlights
Tuberculosis is the second leading infectious cause of mortality worldwide
The first step in the L-leucine biosynthesis is the formation of α-isopropylmalate from acetyl-coenzyme A (CoA) and α-KIV that is catalyzed by αisopropylmalate synthase (α-IPMS). α-isopropylmalate synthase (α-IPMS) is an allosteric enzyme that is present in various organisms like bacteria, fungi and plants
The purified protein was homogenous as indicated by a single protein band on SDS-PAGE1 (Figure 1) and a single peak in ESIMS of molecular mass about 73.1 kDa
Summary
Tuberculosis is the second leading infectious cause of mortality worldwide. Effective drugs against tuberculosis exist, therapy requires prolonged treatment with several drugs, leading to problems in compliance and emergence of multidrug resistance [2]. BMC Structural Biology 2007, 7:39 http://www.biomedcentral.com/1472-6807/7/39 effective drugs against tuberculosis. Development of new drugs and characterization of new targets is urgently required. Mycobacteria synthesize the branched-chain amino acids, L-valine, L-leucine and pantothenic acid from α-ketoisovalerate (α-KIV). The essentiality of this pathway in M. tuberculosis, and its absence in humans makes the enzymes of this pathway attractive target/s for development of drug/s for treatment of tuberculosis [3]. The first step in the L-leucine biosynthesis is the formation of α-isopropylmalate from acetyl-CoA and α-KIV that is catalyzed by αisopropylmalate synthase (α-IPMS). The first step in the L-leucine biosynthesis is the formation of α-isopropylmalate from acetyl-CoA and α-KIV that is catalyzed by αisopropylmalate synthase (α-IPMS). α-IPMS is an allosteric enzyme that is present in various organisms like bacteria, fungi and plants
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