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Proc Natl Acad Sci U S A. 2013 Jul 2;110(27):10922-7. doi: 10.1073/pnas.1213426110. Epub 2013 Jun 19.

Increased enzyme binding to substrate is not necessary for more efficient cellulose hydrolysis.

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  • 1Biomass Conversion Research Laboratory (BCRL), Chemical Engineering and Materials Science, Michigan State University, Lansing, MI 48910, USA.

Abstract

Substrate binding is typically one of the rate-limiting steps preceding enzyme catalytic action during homogeneous reactions. However, interfacial-based enzyme catalysis on insoluble crystalline substrates, like cellulose, has additional bottlenecks of individual biopolymer chain decrystallization from the substrate interface followed by its processive depolymerization to soluble sugars. This additional decrystallization step has ramifications on the role of enzyme-substrate binding and its relationship to overall catalytic efficiency. We found that altering the crystalline structure of cellulose from its native allomorph I(β) to III(I) results in 40-50% lower binding partition coefficient for fungal cellulases, but surprisingly, it enhanced hydrolytic activity on the latter allomorph. We developed a comprehensive kinetic model for processive cellulases acting on insoluble substrates to explain this anomalous finding. Our model predicts that a reduction in the effective binding affinity to the substrate coupled with an increase in the decrystallization procession rate of individual cellulose chains from the substrate surface into the enzyme active site can reproduce our anomalous experimental findings.

KEYWORDS:

biofuels; glycosidases; kinetic modeling; lignocellulose; polysaccharide hydrolysis

PMID:
23784776
[PubMed - indexed for MEDLINE]
PMCID:
PMC3703979
Free PMC Article
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