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Steps for Shigella Gatekeeper MxiC Function in Hierarchical Type III Secretion Regulation.

Steps for Shigella Gatekeeper MxiC Function in Hierarchical Type III Secretion Regulation.
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Roehrich AD, Bordignon E, Mode S, Shen DK, Liu X, Pain M, Murillo I, Martinez-Argudo I, Sessions RB, Blocker AJ,


Roehrich AD, Bordignon E, Mode S, Shen DK, Liu X, Pain M, Murillo I, Martinez-Argudo I, Sessions RB, Blocker AJ, (click to view)

Roehrich AD, Bordignon E, Mode S, Shen DK, Liu X, Pain M, Murillo I, Martinez-Argudo I, Sessions RB, Blocker AJ,

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The Journal of biological chemistry 2016 12 14() pii jbc.M116.746826
Abstract

Type III secretion systems are complex nanomachines used for injection of proteins from Gram-negative bacteria into eukaryotic cells. While 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, next, effector proteins are injected. Hierarchy between these protein classes is mediated by a conserved gate-keeper protein, MxiC in Shigella. As its molecular mechanism of action is still poorly understood, we used its structure to guide site-directed mutagenesis and dissect its function. We identified mutants predominantly affecting all known features of MxiC regulation: 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.

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