CLONING AND EXPRESSION IN SACCHAROMYCES-CEREVISIAE OF A TRICHODERMA-REESEI BETA-MANNANASE GENE CONTAINING A CELLULOSE-BINDING DOMAIN

beta-Mannanase (endo-1,4-beta-mannanase; mannan endo-1,4-beta-mannosid ase; EC 3.2.1.78) catalyzes endo wise hydrolysis of the backbone of ma nnan and heteromannans, including hemicellulose polysaccharides, which are among the major components of plant cell walls. The gene man1, wh ich encodes beta-mannanase, of the filamentous fungus Trichoderma rees ei was isolated from an expression library by using antiserum raised t owards the earlier-purified beta-mannanase protein. The deduced beta m annanase consists of 410 amino acids. On the basis of hydrophobic clus ter analysis, the beta-mannanase was assigned to family 5 of glycosyl hydrolases (cellulase family A). The C terminus of the beta-mannanase has strong amino acid sequence similarity to the cellulose binding dom ains of fungal cellulases and is preceded by a serine-, threonine- and proline-rich region. Consequently, the beta-mannanase is probably org anized similarly to the T. reesei cellulases, having a catalytic core domain separated from the substrate-binding domain by an O-glycosylate d linker. Active beta-mannanase was expressed and secreted by using th e yeast Saccharomyces cerevisiae as the host. The results indicate tha t the man1 gene encodes the two beta-mannanases with different isoelec tric points (pIs 4.6 and 5.4) purified earlier from T. reesei.