Multienzyme complexes organize enzymatic functions into defined architectures to speed transfer of intermediates and facilitate specialized reactions. The cellulosome assembles cellulose-degrading enzymes on the cell surface using a scaffoldin protein containing cohesin domains to anchor enzymes. Sun et al. now explore the portability of this system as well as the differential ability of two scaffoldins to assemble a 'minihemicellulosome' capable of degrading arabinoxylan and birchwood xylan into xylose. The authors generated strains expressing one or more of the hemicellulose-degrading enzymes XynII (an endo-1,4-β-xylanase), XlnD (a β-xylosidase) and AbfB (an α-L-arabinofuranosidase) as well as the scaffoldin CipA1, which contains a single cohesin domain, or CipA3, which contains three cohesin domains. Xylan degradation increased with increasing numbers of enzymes when they were displayed on the multi-cohesin CipA3, but the display of individual enzymes mediated by CipA1 did not yield the same increases in activity. AbfB function was particularly dependent on assembly, with the CipA1 display of all three enzymes only as effective as either the bifunctional XynII-XlnD CipA3 construct or the combined display of XynII and XlnD by CipA1. Integration of the XynII-XlnD CipA3 construct into a xylose-utilizing Saccharomyces cerevisiae strain allowed conversion of birchwood xylan into ethanol, yielding 0.31 g ethanol per g xylan consumed. These results set the stage for further explorations of the role of molecular organization in enzyme function.
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Goodman, C. Assembling activity. Nat Chem Biol 8, 502 (2012). https://doi.org/10.1038/nchembio.979
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DOI: https://doi.org/10.1038/nchembio.979
