title: Steps for Shigella Gatekeeper Protein MxiC Function in Hierarchical Type III Secretion Regulation.
abstract: Type III secretion systems are complex nanomachines used for injection of proteins from Gram-negative bacteria into eukaryotic cells. Although they are assembled when the environmental conditions are appropriate, they only start secreting upon contact with a host cell. Secretion is hierarchical. First, the pore-forming translocators are released. Second, effector proteins are injected. Hierarchy between these protein classes is mediated by a conserved gatekeeper protein, MxiC, in Shigella As its molecular mechanism of action is still poorly understood, we used its structure to guide site-directed mutagenesis and to dissect its function. We identified mutants predominantly affecting all known features of MxiC regulation as follows: secretion of translocators, MxiC and/or effectors. Using molecular genetics, we then mapped at which point in the regulatory cascade the mutants were affected. Analysis of some of these mutants led us to a set of electron paramagnetic resonance experiments that provide evidence that MxiC interacts directly with IpaD. We suggest how this interaction regulates a switch in its conformation that is key to its functions.
authors.affiliation: From the School of Cellular and Molecular Medicine and School of Biochemistry, Medical Sciences Building, Faculty of Medical and Veterinary Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom.
authors.forename: A Dorothea
authors.initials: AD
authors.lastname: Roehrich
authors.affiliation: the Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany.
authors.forename: Enrica
authors.initials: E
authors.lastname: Bordignon
authors.affiliation: From the School of Cellular and Molecular Medicine and School of Biochemistry, Medical Sciences Building, Faculty of Medical and Veterinary Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom.
authors.forename: Selma
authors.initials: S
authors.lastname: Mode
authors.affiliation: From the School of Cellular and Molecular Medicine and School of Biochemistry, Medical Sciences Building, Faculty of Medical and Veterinary Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom.
authors.forename: Da-Kang
authors.initials: DK
authors.lastname: Shen
authors.affiliation: From the School of Cellular and Molecular Medicine and School of Biochemistry, Medical Sciences Building, Faculty of Medical and Veterinary Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom.
authors.forename: Xia
authors.initials: X
authors.lastname: Liu
authors.affiliation: From the School of Cellular and Molecular Medicine and School of Biochemistry, Medical Sciences Building, Faculty of Medical and Veterinary Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom.
authors.forename: Maria
authors.initials: M
authors.lastname: Pain
authors.affiliation: From the School of Cellular and Molecular Medicine and School of Biochemistry, Medical Sciences Building, Faculty of Medical and Veterinary Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom.
authors.forename: Isabel
authors.initials: I
authors.lastname: Murillo
authors.affiliation: From the School of Cellular and Molecular Medicine and School of Biochemistry, Medical Sciences Building, Faculty of Medical and Veterinary Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom; the Área de Genética, Facultad de Ciencias Ambientales y Bioquímica, Universidad de Castilla-La Mancha, E-45071 Toledo, Spain.
authors.forename: Isabel
authors.initials: I
authors.lastname: Martinez-Argudo
authors.affiliation: From the School of Cellular and Molecular Medicine and School of Biochemistry, Medical Sciences Building, Faculty of Medical and Veterinary Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom.
authors.forename: Richard B
authors.initials: RB
authors.lastname: Sessions
authors.affiliation: From the School of Cellular and Molecular Medicine and School of Biochemistry, Medical Sciences Building, Faculty of Medical and Veterinary Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom. Electronic address: ariel.blocker@bristol.ac.uk.
authors.forename: Ariel J
authors.initials: AJ
authors.lastname: Blocker
mesh_terms: D000942:Antigens, Bacterial / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D058947:Bacterial Secretion Systems / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D012763:Shigella flexneri / Q000235:genetics / Q000378:metabolism*
chemical_list: D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D058947:Bacterial Secretion Systems; C095770:IpaD protein, Shigella flexneri
keywords: Gram-negative bacteria; MxiC; Shigella; biophysics; cellular regulation; electron paramagnetic resonance (EPR); molecular genetics; protein secretion; type III secretion system (T3SS)