Abstract
The cellulosome is an intriguing multienzyme complex found in cellulolytic bacteria that plays a key role in the degradation of plant cell-wall polysaccharides. In Ruminococcus flavefaciens, a predominant fiber-degrading bacterium found in ruminants, the cellulosome is anchored to the bacterial cell wall through a relatively short ScaE scaffoldin. Determination of the crystal structure of the lone type-III ScaE cohesin from R. flavefaciens (Rf-CohE) was initiated as a part of a structural effort to define cellulosome assembly. The structure was determined at 1.95 angstrom resolution by single-wavelength anomalous diffraction. This is the first detailed description of a crystal structure for a type-III cohesin, and its features were compared with those of the known type-I and type-II cohesin structures. The Rf-CohE module folds into a nine-stranded beta-sandwich with jellyroll topology, typically observed for cohesins, and includes two beta-flaps in the midst of beta-strands 4 and 8, similar to the type-II cohesin structures. However, the presence in Rf-CohE of an additional 13-residue alpha-helix located between beta-strands 8 and 9 represents a dramatic divergence from other known cohesin structures. The prominent alpha-helix is enveloped by an extensive N-terminal loop, not observed in any other known cohesin, which embraces the helix presumably enhancing its stability. A planar surface at the upper portion of the front face of the molecule, bordered by beta-flap 8, exhibits plausible dimensions and exposed amino acid residues to accommodate the dockerin-binding site. Proteins 2009; 77:699-709. (C) 2009 Wiley-Liss, Inc.
Original language | English |
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Pages (from-to) | 699-709 |
Number of pages | 11 |
Journal | Proteins: Structure, Function, and Bioinformatics |
Volume | 77 |
Issue number | 3 |
Early online date | 18 May 2009 |
DOIs | |
Publication status | Published - 15 Nov 2009 |
Keywords
- cellulose degradation
- multienzyme complex
- type-III cohesin
- dockerin module
- scaffolding protein CIPA
- X-ray characterization
- dual binding mode
- clostridium-thermocellum
- cell-surface
- II cohesin
- gene-cluster
- dockerin interaction
- cellulose-binding
- complex