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This Article Full Text (Papers in Press[PDF]) All Versions of this Article: mic.0.026930-0v1 155/7/2442    most recent Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Dvortsov, I. A Articles by Velikodvorskaya, G. A Search for Related Content PubMed PubMed Citation Articles by Dvortsov, I. A Articles by Velikodvorskaya, G. A Agricola Articles by Dvortsov, I. A Articles by Velikodvorskaya, G. A

Carbohydrate binding properties of a separately folding protein module from β-1,3-glucanase Lic16A of Clostridium thermocellum

¹ Institute of Molecular Genetics RAS;
² Department of Microbiology, Technische Universitaet Muenchen

ABSTRACT

The multi-modular non-cellulosomal endo-1,3(4)-β-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. It did not bind soluble polysaccharides on which Lic16A is highly active. Ca²⁺ ions have 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=3.1·104 M^-1), yeast cell wall glucan (K=1.4·105 M^-1) and chitin (K=3.3·105 M^-1 in the presence of Ca²⁺). Lic16A deletion derivatives lacking CBMX have been characterized by lower affinity to lichenan and laminarin and a slight decrease in optimum temperature and thermostability. However, the specific activity was not significantly affected.

³ E-mail: dvortsov{at}img.ras.ru