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The crystal structure of a type I cohesin domain at 1.7 Å resolution

Abstract : The quaternary organization of the cellulosome, a multi-enzymatic extracellular complex produced by cellulolytic bacteria, depends on specific interactions between dockerin domains, double EF-hand subunits carried by the catalytic components, and cohesin domains, individual receptor subunits linearly arranged within a non-catalytic scaffolding polypeptide. Cohesin-dockerin complexes with distinct specificities are also thought to mediate the attachment of cellulosomes to the cell membrane. We report here the crystal structure of a single cohesin domain from the scaffolding protein of Clostridium thermocellum. The cohesin domain folds into a nine-stranded beta-sandwich with an overall "jelly roll" topology, similar to that observed in bacterial cellulose-binding domains. Surface-exposed patches of conserved residues promote extensive intermolecular contacts in the crystal, and suggest a possible binding target for the EF-hand pair of the cognate dockerin domain. Comparative studies of cohesin domains indicate that, in spite of low sequence similarities and different functional roles, all cohesin domains share a common nine-stranded beta-barrel fold stabilized by a conserved hydrophobic core. The formation of stable cohesin-dockerin complexes requires the presence of Ca2+. However, the structure of the cohesin domain reported here reveals no obvious Ca2+-binding site, and previous experiments have failed to detect high affinity binding of Ca2+ to the unliganded dockerin domain of endoglucanase CelD. Based on structural and biochemical evidence, we propose a model of the cohesin-dockerin complex in which the dockerin domain requires complexation with its cohesin partner for protein stability and high-affinity Ca2+ binding.
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Submitted on : Tuesday, February 9, 2021 - 7:12:41 PM
Last modification on : Thursday, April 7, 2022 - 10:10:29 AM

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Gisele A. Tavares, Pierre Béguin, Pedro M. Alzari. The crystal structure of a type I cohesin domain at 1.7 Å resolution. Journal of Molecular Biology, 1997, 2002-05-25, 273 (3), pp.701-713. ⟨10.1006/jmbi.1997.1326⟩. ⟨pasteur-03136642⟩



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