title: Structural and biochemical characterization of the essential DsbA-like disulfide bond forming protein from Mycobacterium tuberculosis.
abstract: BACKGROUND
  Bacterial Disulfide bond forming (Dsb) proteins facilitate proper folding and disulfide bond formation of periplasmic and secreted proteins. Previously, we have shown that Mycobacterium tuberculosis Mt-DsbE and Mt-DsbF aid in vitro oxidative folding of proteins. The M. tuberculosis proteome contains another predicted membrane-tethered Dsb protein, Mt-DsbA, which is encoded by an essential gene.
  
  
  RESULTS
  Herein, we present structural and biochemical analyses of Mt-DsbA. The X-ray crystal structure of Mt-DsbA reveals a two-domain structure, comprising a canonical thioredoxin domain with the conserved CXXC active site cysteines in their reduced form, and an inserted α-helical domain containing a structural disulfide bond. The overall fold of Mt-DsbA resembles that of other DsbA-like proteins and not Mt-DsbE or Mt-DsbF. Biochemical characterization demonstrates that, unlike Mt-DsbE and Mt-DsbF, Mt-DsbA is unable to oxidatively fold reduced, denatured hirudin. Moreover, on the substrates tested in this study, Mt-DsbA has disulfide bond isomerase activity contrary to Mt-DsbE and Mt-DsbF.
  
  
  CONCLUSIONS
  These results suggest that Mt-DsbA acts upon a distinct subset of substrates as compared to Mt-DsbE and Mt-DsbF. One could speculate that Mt-DsbE and Mt-DsbF are functionally redundant whereas Mt-DsbA is not, offering an explanation for the essentiality of Mt-DsbA in M. tuberculosis.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Chim
authors.forename: Christine A
authors.initials: CA
authors.lastname: Harmston
authors.forename: David J
authors.initials: DJ
authors.lastname: Guzman
authors.affiliation: Departments of Molecular Biology and Biochemistry, UCI, Irvine, CA 92697, USA. celia.goulding@uci.edu.
authors.forename: Celia W
authors.initials: CW
authors.lastname: Goulding
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D003545:Cysteine / Q000737:chemistry* / Q000378:metabolism; D004220:Disulfides / Q000737:chemistry / Q000378:metabolism; D005798:Genes, Bacterial; D007535:Isomerases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009169:Mycobacterium tuberculosis / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D010088:Oxidoreductases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D058849:Protein Refolding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D020543:Proteome; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D013879:Thioredoxins / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D004220:Disulfides; D020543:Proteome; D013879:Thioredoxins; D010088:Oxidoreductases; D007535:Isomerases; D003545:Cysteine