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

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.

Tavares GA ，Béguin P ，Alzari PM 《JOURNAL OF MOLECULAR BIOLOGY》

Insights into the structural determinants of cohesin-dockerin specificity revealed by the crystal structure of the type II cohesin from Clostridium thermocellum SdbA.

Carvalho AL ，Pires VM ，Gloster TM ，Turkenburg JP ，Prates JA ，Ferreira LM ，Romão MJ ，Davies GJ ，Fontes CM ，Gilbert HJ ... -  《JOURNAL OF MOLECULAR BIOLOGY》

Crystal structure of a cohesin module from Clostridium cellulolyticum: implications for dockerin recognition.

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.

Spinelli S ，Fiérobe HP ，Belaïch A ，Belaïch JP ，Henrissat B ，Cambillau C ... -  《JOURNAL OF MOLECULAR BIOLOGY》

The cellulosome: an exocellular, multiprotein complex specialized in cellulose degradation.

Béguin P ，Lemaire M 《-》

Structural characterization of type II dockerin module from the cellulosome of Clostridium thermocellum: calcium-induced effects on conformation and target recognition.

Adams JJ ，Webb BA ，Spencer HL ，Smith SP ... -  《BIOCHEMISTRY》