title: Crystal structure of a cohesin module from Clostridium cellulolyticum: implications for dockerin recognition.
abstract: In the assembly of the Clostridium cellulolyticum cellulosome, the multiple cohesin modules of the scaffolding protein CipC serve as receptors for cellulolytic enzymes which bear a dockerin module. The X-ray structure of a type I C. cellulolyticum cohesin module (Cc-cohesin) has been solved using molecular replacement, and refined at 2.0 A resolution. Despite a rather low sequence identity of 32 %, this module has a fold close to those of the two Clostridium thermocellum cohesin (Ct-cohesin) modules whose 3D structures have been determined previously. Cc-cohesin forms a dimer in the crystal, as do the two Ct-cohesins. We show here that the dimer exists in solution and that addition of dockerin-containing proteins dissociates the dimer. This suggests that the dimerization interface and the cohesin/dockerin interface may overlap. The nature of the overall surface and of the dimer interface of Cc-cohesin differ notably from those of the Ct-cohesin modules, being much less polar, and this may explain the species specificity observed in the cohesin/dockerin interaction of C. cellulolyticum and C. thermocellum. We have produced a topology model of a C. cellulolyticum dockerin and of a Cc-cohesin/dockerin complex using homology modeling and available biochemical data. Our model suggests that a special residue pair, already identified in dockerin sequences, is located at the center of the cohesin surface putatively interacting with the dockerin.
authors.affiliation: Architecture et Fonction des Macromolécules Biologiques, UMR 6098, CNRS-Universités de Marseille I et II, 31 Chemin Joseph-Aiguier, Marseille, Cedex 20, 13402, France.
authors.forename: S
authors.initials: S
authors.lastname: Spinelli
authors.forename: H P
authors.initials: HP
authors.lastname: Fiérobe
authors.forename: A
authors.initials: A
authors.lastname: Belaïch
authors.forename: J P
authors.initials: JP
authors.lastname: Belaïch
authors.forename: B
authors.initials: B
authors.lastname: Henrissat
authors.forename: C
authors.initials: C
authors.lastname: Cambillau
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism*; D002850:Chromatography, Gel; D003013:Clostridium / Q000737:chemistry*; D018360:Crystallography, X-Ray; D019281:Dimerization; D008565:Membrane Proteins / Q000737:chemistry; D008954:Models, Biological; D008958:Models, Molecular; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010446:Peptide Fragments / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D013045:Species Specificity; D013379:Substrate Specificity
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; C080369:CipA protein, Clostridium; C098847:CipC protein, Clostridium cellulolyticum; D008565:Membrane Proteins; D010446:Peptide Fragments