| Autor: |
Dvortsov IA; Institute of Molecular Genetics RAS, 2 Kurchatov Square, 123182 Moscow, Russian Federation., Lunina NA; Institute of Molecular Genetics RAS, 2 Kurchatov Square, 123182 Moscow, Russian Federation., Chekanovskaya LA; Institute of Molecular Genetics RAS, 2 Kurchatov Square, 123182 Moscow, Russian Federation., Schwarz WH; Department of Microbiology, Technische Universität München, Am Hochanger 4, D-85350 Freising-Weihenstephan, Germany., Zverlov VV; Department of Microbiology, Technische Universität München, Am Hochanger 4, D-85350 Freising-Weihenstephan, Germany.; Institute of Molecular Genetics RAS, 2 Kurchatov Square, 123182 Moscow, Russian Federation., Velikodvorskaya GA; Institute of Molecular Genetics RAS, 2 Kurchatov Square, 123182 Moscow, Russian Federation. |
| Abstrakt: |
The multi-modular non-cellulosomal endo-1,3(4)-beta-glucanase Lic16A from Clostridium thermocellum contains a so-called X module (denoted as CBMX) near the N terminus of the catalytic module (191-426 aa). Melting of X-module-containing recombinant proteins revealed an independent folding of the module. CBMX was isolated and studied as a separate fragment. It was shown to bind to various insoluble polysaccharides, including xylan, pustulan, chitin, chitosan, yeast cell wall glucan, Avicel and bacterial crystalline cellulose. CBMX thus contains a hitherto unknown carbohydrate-binding module (CBM54). It did not bind soluble polysaccharides on which Lic16A is highly active. Ca2+ ions had effects on the binding, e.g. stimulated complex formation with chitosan, which was observed only in the presence of Ca2+. The highest affinity to CBMX was shown for xylan (binding constant K=3.1x10(4) M(-1)), yeast cell wall glucan (K=1.4x10(5) M(-1)) and chitin (K=3.3.10(5) M(-1) in the presence of Ca2+). Lic16A deletion derivatives lacking CBMX had lower affinity to lichenan and laminarin and a slight decrease in optimum temperature and thermostability. However, the specific activity was not significantly affected. |
