title: Cleavage of the moaX-encoded fused molybdopterin synthase from Mycobacterium tuberculosis is necessary for activity.
abstract: BACKGROUND
  Molybdopterin cofactor (MoCo) biosynthesis in Mycobacterium tuberculosis is associated with a multiplicity of genes encoding several enzymes in the pathway, including the molybdopterin (MPT) synthase, a hetero tetramer comprising two MoaD and two MoaE subunits. In addition to moaD1, moaD2, moaE1, moaE2, the M. tuberculosis genome also contains a moaX gene which encodes an MPT-synthase in which the MoaD and MoaE domains are located on a single polypeptide. In this study, we assessed the requirement for post-translational cleavage of MoaX for functionality of this novel, fused MPT synthase and attempted to establish a functional hierarchy for the various MPT-synthase encoding genes in M. tuberculosis.
  
  
  RESULTS
  Using a heterologous Mycobacterium smegmatis host and the activity of the MoCo-dependent nitrate reductase, we confirmed that moaD2 and moaE2 from M. tuberculosis together encode a functional MPT synthase. In contrast, moaD1 displayed no functionality in this system, even in the presence of the MoeBR sulphurtransferase, which contains the rhodansese-like domain, predicted to activate MoaD subunits. We demonstrated that cleavage of MoaX into its constituent MoaD and MoaE subunits was required for MPT synthase activity and confirmed that cleavage occurs between the Gly82 and Ser83 residues in MoaX. Further analysis of the Gly81-Gly82 motif confirmed that both of these residues are necessary for catalysis and that the Gly81 was required for recognition/cleavage of MoaX by an as yet unidentified protease. In addition, the MoaE component of MoaX was able to function in conjunction with M. smegmatis MoaD2 suggesting that cleavage of MoaX renders functionally interchangeable subunits. Expression of MoaX in E. coli revealed that incorrect post-translational processing is responsible for the lack of activity of MoaX in this heterologous host.
  
  
  CONCLUSIONS
  There is a degree of functional interchangeability between the MPT synthase subunits of M. tuberculosis. In the case of MoaX, post-translational cleavage at the Gly82 residue is required for function.
authors: DST/NRF Centre of Excellence for Biomedical TB Research, Faculty of Health Sciences, University of the Witwatersrand, National Health Laboratory Service, P.O. Box 1038, Johannesburg, 2000, South Africa. Nicole.Narrandes@nhls.ac.za.
authors: Nicole C
authors: NC
authors: Narrandes
authors: DST/NRF Centre of Excellence for Biomedical TB Research, Faculty of Health Sciences, University of the Witwatersrand, National Health Laboratory Service, P.O. Box 1038, Johannesburg, 2000, South Africa. Edith.Machowski@nhls.ac.za.
authors: Edith Erika
authors: EE
authors: Machowski
authors: MRC/NHLS/UCT Molecular Mycobacteriology Research Unit and DST/NRF Centre of Excellence for Biomedical TB Research, Institute of Infectious Disease & Molecular Medicine and Division of Medical Microbiology, University of Cape Town, Cape Town, South Africa. Valerie.Mizrahi@uct.ac.za.
authors: Valerie
authors: V
authors: Mizrahi
authors: DST/NRF Centre of Excellence for Biomedical TB Research, Faculty of Health Sciences, University of the Witwatersrand, National Health Laboratory Service, P.O. Box 1038, Johannesburg, 2000, South Africa. bavesh.kana@nhls.ac.za.
authors: Bavesh D
authors: BD
authors: Kana
mesh_terms: D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D020102:Mycobacterium smegmatis / Q000235:genetics / Q000378:metabolism; D009169:Mycobacterium tuberculosis / Q000201:enzymology*; D011499:Protein Processing, Post-Translational; D059748:Proteolysis; D013466:Sulfurtransferases / Q000378:metabolism*
chemical_list: D013466:Sulfurtransferases; C085585:molybdopterin synthase
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