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Combined Crystal Structure of a Type I Cohesin: Mutation and Affinity Binding Studies Reveal Structural Determinants of Cohesin-Dockerin Specificities

Lookup NU author(s): Kate Cameron, Emeritus Professor Harry Gilbert

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Abstract

Background: Cellulosomal cohesin-dockerin types are reversed in Bacteroides cellulosolvens. Results: Combined crystallographic and computational approaches of a lone cohesin yielded a structural model of the cohesin-dockerin complex that was verified experimentally. Conclusion: The dockerin dual-binding mode is not exclusive to enzyme integration into cellulosomes; it also characterizes cell-surface attachment. Significance: This combined approach provides a platform for generating testable hypotheses of the high affinity cohesin-dockerin interaction.Cohesin-dockerin interactions orchestrate the assembly of one of nature's most elaborate multienzyme complexes, the cellulosome. Cellulosomes are produced exclusively by anaerobic microbes and mediate highly efficient hydrolysis of plant structural polysaccharides, such as cellulose and hemicellulose. In the canonical model of cellulosome assembly, type I dockerin modules of the enzymes bind to reiterated type I cohesin modules of a primary scaffoldin. Each type I dockerin contains two highly conserved cohesin-binding sites, which confer quaternary flexibility to the multienzyme complex. The scaffoldin also bears a type II dockerin that anchors the entire complex to the cell surface by binding type II cohesins of anchoring scaffoldins. In Bacteroides cellulosolvens, however, the organization of the cohesin-dockerin types is reversed, whereby type II cohesin-dockerin pairs integrate the enzymes into the primary scaffoldin, and type I modules mediate cellulosome attachment to an anchoring scaffoldin. Here, we report the crystal structure of a type I cohesin from B. cellulosolvens anchoring scaffoldin ScaB to 1.84-angstrom resolution. The structure resembles other type I cohesins, and the putative dockerin-binding site, centered at -strands 3, 5, and 6, is likely to be conserved in other B. cellulosolvens type I cohesins. Combined computational modeling, mutagenesis, and affinity-based binding studies revealed similar hydrogen-bonding networks between putative Ser/Asp recognition residues in the dockerin at positions 11/12 and 45/46, suggesting that a dual-binding mode is not exclusive to the integration of enzymes into primary cellulosomes but can also characterize polycellulosome assembly and cell-surface attachment. This general approach may provide valuable structural information of the cohesin-dockerin interface, in lieu of a definitive crystal structure.

Publication metadata

Author(s): Cameron K, Weinstein JY, Zhivin O, Bule P, Fleishman SJ, Alves VD, Gilbert HJ, Ferreira LMA, Fontes CMGA, Bayer EA, Najmudin S

Publication type: Article

Publication status: Published

Journal: Journal of Biological Chemistry

Year: 2015

Volume: 290

Issue: 26

Pages: 16215-16225

Print publication date: 26/06/2015

Online publication date: 01/05/2015

ISSN (print): 0021-9258

ISSN (electronic): 1083-351X

Publisher: American Society for Biochemistry and Molecular Biology

URL: http://dx.doi.org/10.1074/jbc.M115.653303

DOI: 10.1074/jbc.M115.653303

PubMed id: 25934389

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