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Publication Abstract from PubMed

BACKGROUND: is one of the predominant fiber-degrading bacteria found in the rumen of herbivores. Bioinformatic analysis of the recently sequenced genome indicated that this bacterium produces one of the most intricate cellulosome systems known to date. A distinct ORF, encoding for a multi-modular protein, RflaF_05439, was discovered during mining of the genome sequence. It is composed of two tandem modules of currently undefined function that share 45% identity and a C-terminal X-dockerin modular dyad. Gaining insight into the diversity, architecture and organization of different types of proteins in the cellulosome system is essential for broadening our understanding of a multi-enzyme complex, considered to be one of the most efficient systems for plant cell wall polysaccharide degradation in nature. METHODOLOGYPRINCIPAL FINDINGS: Following bioinformatic analysis, the second tandem module of RflaF_05439 was cloned and its selenium-labeled derivative was expressed and crystallized. The crystals belong to space group P2 with unit-cell parameters of = 65.81, = 60.61, = 66.13 A, beta = 107.66 degrees and contain two protein molecules in the asymmetric unit. The crystal structure was determined at 1.38-A resolution by X-ray diffraction using the single-wavelength anomalous dispersion (SAD) method and was refined to R and R of 0.127 and 0.152 respectively. The protein molecule mainly comprises a beta-sheet flanked by short alpha-helixes, and a globular alpha-helical domain. The structure was found to be structurally similar to members of the NlpC/P60 superfamily of cysteine peptidases. CONCLUSIONSSIGNIFICANCE: The 3D structure of the second repeat of the RflaF_05439 enabled us to propose a role for the currently undefined function of this protein. Its putative function as a cysteine peptidase is inferred from structural homology studies. It is therefore apparent that cellulosomes integrate proteins with other functions in addition to the classic well-defined carbohydrate active enzymes.

Crystal Structure of an Uncommon Cellulosome-Related Protein Module from Ruminococcus flavefaciens That Resembles Papain-Like Cysteine Peptidases.,Levy-Assaraf M, Voronov-Goldman M, Rozman Grinberg I, Weiserman G, Shimon LJ, Jindou S, Borovok I, White BA, Bayer EA, Lamed R, Frolow F PLoS One. 2013;8(2):e56138. doi: 10.1371/journal.pone.0056138. Epub 2013 Feb 14. PMID:23457513^[1]

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