Cohesin diversity revealed by the crystal structure of the anchoring cohesin from Ruminococcus flavefaciens

Authors

  • Orly Alber,

    1. Department of Biological Chemistry, The Weizmann Institute of Science, Rehovot 76100, Israel
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  • Ilit Noach,

    1. Department of Biological Chemistry, The Weizmann Institute of Science, Rehovot 76100, Israel
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  • Marco T. Rincon,

    1. Microbial Ecology Group, Rowett Institute of Nutrition and Health, University of Aberdeen, Bucksburn, Aberdeen AB21 9SB, United Kingdom
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  • Harry J. Flint,

    1. Microbial Ecology Group, Rowett Institute of Nutrition and Health, University of Aberdeen, Bucksburn, Aberdeen AB21 9SB, United Kingdom
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  • Linda J. W. Shimon,

    1. Department of Chemical Services, The Weizmann Institute of Science, Rehovot 76100, Israel
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  • Raphael Lamed,

    1. Department of Molecular Microbiology and Biotechnology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv 69978, Israel
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  • Felix Frolow,

    Corresponding author
    1. Department of Molecular Microbiology and Biotechnology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv 69978, Israel
    2. The Daniella Rich Institute for Structural Biology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv 69978, Israel
    • Department of Molecular Microbiology and Biotechnology, Tel Aviv University, Ramat Aviv 69978, Israel
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  • Edward A. Bayer

    Corresponding author
    1. Department of Biological Chemistry, The Weizmann Institute of Science, Rehovot 76100, Israel
    • Department of Biological Chemistry, The Weizmann Institute of Science, Rehovot 76100 Israel
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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 Å 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 β-sandwich with jellyroll topology, typically observed for cohesins, and includes two β-flaps in the midst of β-strands 4 and 8, similar to the type-II cohesin structures. However, the presence in Rf-CohE of an additional 13-residue α-helix located between β-strands 8 and 9 represents a dramatic divergence from other known cohesin structures. The prominent α-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 byβ-flap 8, exhibits plausible dimensions and exposed amino acid residues to accommodate the dockerin-binding site. Proteins 2009. © 2009 Wiley-Liss, Inc.

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