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pH profiles of cellulases depend on the substrate and architecture of the binding region
Author(s) -
Røjel Nanna,
Kari Jeppe,
Sørensen Trine H.,
Borch Kim,
Westh Peter
Publication year - 2020
Publication title -
biotechnology and bioengineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.136
H-Index - 189
eISSN - 1097-0290
pISSN - 0006-3592
DOI - 10.1002/bit.27206
Subject(s) - cellulase , trichoderma reesei , chemistry , substrate (aquarium) , cellulose , enzyme , glycoside hydrolase , stereochemistry , biochemistry , biology , ecology
Understanding the pH effect of cellulolytic enzymes is of great technological importance. In this study, we have examined the influence of pH on activity and stability for central cellulases (Cel7A, Cel7B, Cel6A from Trichoderma reesei , and Cel7A from Rasamsonia emersonii ). We systematically changed pH from 2 to 7, temperature from 20°C to 70°C, and used both soluble (4‐nitrophenyl β‐ d ‐lactopyranoside [pNPL]) and insoluble (Avicel) substrates at different concentrations. Collective interpretation of these data provided new insights. An unusual tolerance to acidic conditions was observed for both investigated Cel7As, but only on real insoluble cellulose. In contrast, pH profiles on pNPL were bell‐shaped with a strong loss of activity both above and below the optimal pH for all four enzymes. On a practical level, these observations call for the caution of the common practice of using soluble substrates for the general characterization of pH effects on cellulase activity. Kinetic modeling of the experimental data suggested that the nucleophile of Cel7A experiences a strong downward shift in pK a upon complexation with an insoluble substrate. This shift was less pronounced for Cel7B, Cel6A, and for Cel7A acting on the soluble substrate, and we hypothesize that these differences are related to the accessibility of water to the binding region of the Michaelis complex.