VISUALIZATION OF THE ADSORPTION OF A BACTERIAL ENDO-BETA-1,4-GLUCANASE AND ITS ISOLATED CELLULOSE-BINDING DOMAIN TO CRYSTALLINE CELLULOSE

Endo-beta-1,4-glucanase A (CenA), a cellulase from the bacterium Cellu lomonas fimi, is composed of two domains: a catalytic domain and a cel lulose-binding domain. Adsorption of CenA and its isolated cellulose-b inding domain (CBD-PT(CenA)) to Valonia cellulose microcrystals was ex amined by transmission electron microscopy using an antibody sandwich technique (CenA/CBD.PT(CenA)-alphaCenA IgG-protein A-gold conjugate). Adsorption of both CenA and CBD-PT(CenA) occurred along the lengths of the microcrystals, with an apparent preference for certain crystal fa ces or edges. CenA or CBD.PT(CenA), but not the isolated catalytic dom ain, were shown to prevent the flocculation of microcrystalline bacter ial cellulose. The cellulose-binding domain may assist crystalline cel lulose hydrolysis in vitro by promoting substrate dispersion.