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Instruments / Technical Area	Publication Details	Published	Actions
I04-Macromolecular Crystallography	EssC: domain structures inform on the elusive translocation channel in the Type VII secretion system Martin Zoltner , Wui M. A. V. Ng , Jillian J. Money , Paul K. Fyfe , Holger Kneuper , Tracy Palmer , William N. Hunter Biochemical Journal 473, 1941 - 1952 DOI: 10.1042/BCJ20160257 Diamond Proposal Number(s): [10071] Open Access Show Abstract ▼ Abstract: The membrane-bound protein EssC is an integral component of the bacterial Type VII secretion system (T7SS), which is a determinant of virulence in important Gram-positive pathogens. The protein is predicted to consist of an intracellular repeat of forkhead-associated (FHA) domains at the N-terminus, two transmembrane helices and three P-loop-containing ATPase-type domains, D1–D3, forming the C-terminal intracellular segment. We present crystal structures of the N-terminal FHA domains (EssC-N) and a C-terminal fragment EssC-C from Geobacillus thermodenitrificans, encompassing two of the ATPase-type modules, D2 and D3. Module D2 binds ATP with high affinity whereas D3 does not. The EssC-N and EssC-C constructs are monomeric in solution, but the full-length recombinant protein, with a molecular mass of approximately 169 kDa, forms a multimer of approximately 1 MDa. The observation of protomer contacts in the crystal structure of EssC-C together with similarity to the DNA translocase FtsK, suggests a model for a hexameric EssC assembly. Such an observation potentially identifies the key, and to date elusive, component of pore formation required for secretion by this recently discovered secretion system. The juxtaposition of the FHA domains suggests potential for interacting with other components of the secretion system. The structural data were used to guide an analysis of which domains are required for the T7SS machine to function in pathogenic Staphylococcus aureus. The extreme C-terminal ATPase domain appears to be essential for EssC activity as a key part of the T7SS, whereas D2 and FHA domains are required for the production of a stable and functional protein.	Jun 2016
I03-Macromolecular Crystallography	Structures of bacterial kynurenine formamidase reveal a crowded binuclear-zinc catalytic site primed to generate a potent nucleophile. Laura Diaz Saez , Kannan Srikannathasan , Martin Zoltner , William Hunter Biochemical Journal 462, 581589 DOI: 10.1042/BJ20140511 PMID: 24942958 Open Access Show Abstract ▼ Abstract: Tryptophan is an important precursor for chemical entities that ultimately support the biosynthesis of key metabolites. The second stage of tryptophan catabolism is catalyzed by kynurenine formamidase, an enzyme that is different between eukaryotes and prokaryotes. Here, we characterize the catalytic properties and present the crystal structures of three bacterial kynurenine formamidases. The structures reveal a new amidase protein fold, a highly organized and distinctive binuclear Zn2+ catalytic centre in a confined, hydrophobic and relatively rigid active site. The structure of a complex with 2-aminoacetophenone delineates aspects of molecular recognition extending to the observation that the substrate itself may be conformationally restricted to assist binding in the confined space of the active site and for subsequent processing. The cations occupy a crowded environment and unlike most Zn2+-dependent enzymes there is little scope to increase coordination number during catalysis. We propose that the presence of a bridging water/hydroxide ligand in conjunction with the placement of an active site histidine supports a distinctive amidation mechanism.	Jun 2014

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