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

Dahai Gao, Shishir P.S. Chundawat, Anurag Sethi, Venkatesh Balan, S. Gnanakaran, Bruce E. Dale

Research output: Contribution to journalArticle

86 Scopus citations

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 Iβ 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.

Original languageEnglish (US)
Pages (from-to)10922-10927
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume110
Issue number27
DOIs
StatePublished - Jul 2 2013
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • General

Keywords

  • Biofuels
  • Glycosidases
  • Kinetic modeling
  • Lignocellulose
  • Polysaccharide hydrolysis

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