Insights into the Structural Determinants of Cohesin—Dockerin Specificity Revealed by the Crystal Structure of the Type II Cohesin from Clostridium thermocellum SdbA

• Published in: Journal of molecular biology Vol. 349; no. 5; pp. 909 - 915
• Main Authors: Carvalho, Ana L., Pires, Virginia M.R., Gloster, Tracey M., Turkenburg, Johan P., Prates, José A.M., Ferreira, Luís M.A., Romão, Maria J., Davies, Gideon J., Fontes, Carlos M.G.A., Gilbert, Harry J.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 24.06.2005
• Subjects: Amino Acid Sequence; Bacterial Proteins - chemistry; Binding Sites; cell-attachment; cellulosome; Cellulosomes - chemistry; Clostridium thermocellum; Clostridium thermocellum - chemistry; cohesin; Crystallography, X-Ray; dockerin; Membrane Proteins - chemistry; Models, Molecular; Molecular Sequence Data; plant cell wall; Protein Binding; Protein Structure, Tertiary; Recombinant Proteins - chemistry; cohesin; cell-attachment; cellulosome; CohII; dockerin; plant cell wall; CBM
• ISSN: 0022-2836; 1089-8638
• DOI: 10.1016/j.jmb.2005.04.037

The plant cell wall degrading enzymes expressed by anaerobic microorganisms form large multienzyme complexes (cellulosomes). Cellulosomes assemble by the Type I dockerins on the catalytic subunits binding to the reiterated Type I cohesins in the molecular scaffold, while Type II dockerin–cohesin interactions anchor the complex onto the bacterial cell surface. Type I and Type II cohesin, dockerin pairs show no cross-specificity. Here we report the crystal structure of the Type II cohesin (CohII) from the Clostridium thermocellum cell surface anchoring protein SdbA. The protein domain contains nine β-strands and a small α-helix. The β-strands assemble into two elongated β-sheets that display a typical jelly roll fold. The structure of CohII is very similar to Type I cohesins, and the dockerin binding site, which is centred at β-strands 3, 5 and 6, is likely to be conserved in the two proteins. Subtle differences in the topology of the binding sites and a lack of sequence identity in the β-strands that comprise the core of the dockerin binding site explain why Type I and Type II cohesins display such distinct specificities for their target dockerins.