4fl4

Publication Abstract from PubMed

Cellulosomes are multi-enzyme complexes responsible for efficient degradation of plant cell wall polysaccharides. The non-enzymatic scaffoldin subunit provides a platform for cellulolytic enzyme binding that enhances the overall activity of the bound enzymes. Understanding the unique quaternary structural elements responsible for the enzymatic synergy of the cellulosome is hindered by the large size and inherent flexibility of these multi-protein complexes. Herein, we have used X-ray crystallography, small angle X-ray scattering (SAXS), and molecular dynamics (MD) to structurally characterize a ternary protein complex from the Clostridium thermocellum cellulosome that comprises a C-terminal trimodular fragment of the CipA scaffoldin bound to the SdbA type-II cohesin module and the type-I dockerin module from the Cel9D glycoside hydrolase. This complex represents the largest fragment of the cellulosome solved by X-ray crystallography to date and reveals two rigid domains, formed by the type-I cohesin:dockerin complex and by the X module-type-II cohesin:dockerin complex, which are separated by a 13-residue linker in an extended conformation. The type-I dockerin modules of the four structural models found in the asymmetric unit are in an alternate orientation to that previously observed, which provides further direct support for the dual mode of binding. Conserved intermolecular contacts between symmetry-related complexes were also observed and may play a role in higher order cellulosome structure. SAXS and MD simulations of the ternary complex revealed that the 13-residue intermodular linker of the scaffoldin subunit is highly dynamic in solution. These studies provide fundamental insights into modular positioning, linker flexibility, and higher order organization of the cellulosome.

Scaffoldin conformation and dynamics revealed by a ternary complex from the Clostridium thermocellum cellulosome.,Currie MA, Adams JJ, Faucher F, Bayer EA, Jia Z, Smith SP J Biol Chem. 2012 Jun 15. PMID:22707718^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.