Combination of two separate binding domains defines stoichiometry between type III secretion system chaperone IpgC and translocator protein IpaB |
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Authors: | Lokareddy Ravi Kumar Lunelli Michele Eilers Björn Wolter Vivien Kolbe Michael |
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Institution: | Department of Cellular Microbiology, Max-Planck-Institute for Infection Biology, 10117 Berlin, Germany. |
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Abstract: | Type III secretion systems (TTSSs) utilized by enteropathogenic bacteria require the presence of small, acidic virulence-associated chaperones for effective host cell infection. We adopted a combination of biochemical and cellular techniques to define the chaperone binding domains (CBDs) in the translocators IpaB and IpaC associated with the chaperone IpgC from Shigella flexneri. We identified a novel CBD in IpaB and furthermore precisely mapped the boundaries of the CBDs in both translocator proteins. In IpaC a single binding domain associates with IpgC. In IpaB, we show that the binding of the newly characterized CBD is essential in maintaining the ternary arrangement of chaperone-translocator complex. This hitherto unknown function is reflected in the co-crystal structure as well, with an IpgC dimer bound to an IpaB fragment comprising both CBDs. Moreover, in the absence of this novel CBD the IpaB/IpgC complex aggregates. This dual-recognition of a domain in the protein by the chaperone in facilitating the correct chaperone-substrate organization describes a new function for the TTSS associated chaperone-substrate complexes. |
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Keywords: | Bacteria Chaperone Chaperonin Crystal Structure Membrane Proteins Protein Crosslinking Protein Secretion Protein-Protein Interactions |
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