Cysteine synthase (CysM) of Mycobacterium tuberculosis is an O-phosphoserine sulfhydrylase: Evidence for an alternative cysteine biosynthesis pathway in Mycobacteria
ABSTRACT The biosynthesis of cysteine is a crucial metabolic pathway supplying a building block for de novo protein synthesis but also a reduced thiol as a component of the oxidative defense mechanisms that appear particularly vital in the dormant state of Mycobacterium tuberculosis. We here show that the cysteine synthase CysM is, in contrast to previous annotations, an O-phosphoserine-specific cysteine synthase. CysM belongs to the fold type II pyridoxal 5'-phosphate-dependent enzymes, as revealed by the crystal structure determined at 2.1-angstroms resolution. A model of O-phosphoserine bound to the enzyme suggests a hydrogen bonding interaction of the side chain of Arg220 with the phosphate group as a key feature in substrate selectivity. Replacement of this residue results in a significant loss of specificity for O-phosphoserine. Notably, reactions with sulfur donors are not affected by the amino acid replacement. The specificity of CysM toward O-phosphoserine together with the previously established novel mode of sulfur delivery via thiocarboxylated CysO (Burns, K. E., Baumgart, S., Dorrestein, P. C., Zhai, H., McLafferty, F. W., and Begley, T. P. (2005) J. Am. Chem. Soc. 127, 11602-11603) provide strong evidence for an O-phosphoserine-based cysteine biosynthesis pathway in M. tuberculosis that is independent of both O-acetylserine and the sulfate reduction pathway. The existence of an alternative biosynthetic pathway to cysteine in this pathogen has implications for the design strategy aimed at inhibition of this metabolic route.
- SourceAvailable from: sciencedirect.com
[Show abstract] [Hide abstract]
- "Diffraction quality crystals of CysM were obtained using the protocol as described . Before data collection crystals were flash-frozen in liquid nitrogen, without the addition of any cryoprotectants . "
ABSTRACT: A new crystal structure of the dimeric cysteine synthase CysM from Mycobacterium tuberculosis reveals an open and a closed conformation of the enzyme. In the closed conformation the five carboxy-terminal amino acid residues are inserted into the active site cleft. Removal of this segment results in a decreased lifetime of the alpha-aminoacrylate reaction intermediate, an increased sensitivity to oxidants such as hydrogen peroxide, and loss of substrate selectivity with respect to the sulfur carrier thiocarboxylated CysO. These results highlight features of CysM that might be of particular importance for cysteine biosynthesis under oxidative stress in M. tuberculosis.FEBS letters 01/2009; 583(2):330-6. DOI:10.1016/j.febslet.2008.12.019 · 3.34 Impact Factor
Conference Paper: The discrete model for incident detection using mobile phones[Show abstract] [Hide abstract]
ABSTRACT: It is generally agreed that the current automatic incident detection algorithms do not achieve the desirable levels. The widespread adoption of mobile phone use among the motoring public suggests considerable potential for incident reporting through mobile phones. The primary advantages of mobile phones are their low cost compared with the cost of a network-wide sensing system. And they are abundant. In this paper, we first explore an approach to simulate incident detection via mobile phone based on a stochastic modeling of section-wide lane traffic systems, which is the real-time estimation of the incident-induced traffic congestion and then discuss the numerical results.Intelligent Transportation Systems, 2003. Proceedings. 2003 IEEE; 11/2003
Conference Paper: Min-Max MPC using a tractable QP Problem[Show abstract] [Hide abstract]
ABSTRACT: Min-Max MPC (MMMPC) controllers  suffer from a great computational burden that is often circumvented by using upper bounds of the worst possible case of a performance index. These upper bounds are usually computed by means of linear matrix inequalities (LMI) techniques. In this paper a more efficient approach is shown. This paper proposes a computationally efficient MMMPC control strategy in which a close approximation of the solution of the min-max problem is computed using a quadratic programming problem. The overall computational burden is much lower than that of the min-max problem and the resulting control is shown to have guaranteed stability. Simulation examples are given in the paper.Decision and Control, 2005 and 2005 European Control Conference. CDC-ECC '05. 44th IEEE Conference on; 01/2006