期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 110, 期 27, 页码 10922-10927出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1213426110
关键词
biofuels; kinetic modeling; lignocellulose; polysaccharide hydrolysis; glycosidases
资金
- National Advanced Biofuels Consortium (NABC)
- Center for Nonlinear Studies, and the Laboratory Directed Research and Development (LDRD)
- Los Alamos National Laboratory (LANL)
- US Department of Energy, Office of Science
- Office of Biological and Environmental Research through Cooperative Agreement [DE-FC02-07ER64494]
- University of Wisconsin System
- US Department of Energy
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-beta to IIII 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.
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