title: Enhancement of the endo-beta-1,4-glucanase activity of an exocellobiohydrolase by deletion of a surface loop.
abstract: In the commonly accepted mechanism for enzymatic hydrolysis of cellulose, endo-beta-1,4-glucanases randomly cleave glucosidic bonds within glucan polymers, providing sites for attack by exo-cellobiohydrolases (EC 3.2.1.91). It has been proposed that hydrolysis by Trichoderma reesei cellobiohydrolase II is restricted to the ends of cellulose polymers because two surface loops cover its active site to form a tunnel. In a closely related endoglucanase, E2 from Thermomonospora fusca, access to the substrate appears to be relatively unhindered because the carboxyl-proximal loop is shortened, and the amino-proximal loop is displaced. The hypothesis was examined by deletion of a region in Cellulomonas fimi cellobiohydrolase A corresponding to part of the carboxyl-proximal loop of T. reesei cellobiohydrolase II. The mutation enhanced the endoglucanase activity of the enzyme on soluble O-(carboxymethyl)cellulose and altered its activities on 2',4'-dinitrophenyl-beta-D-cellobioside, insoluble cellulose, and cellotetraose.
authors.affiliation: Department of Microbiology and Immunology, University of British Columbia, Vancouver, Canada.
authors.forename: A
authors.initials: A
authors.lastname: Meinke
authors.forename: H G
authors.initials: HG
authors.lastname: Damude
authors.forename: P
authors.initials: P
authors.lastname: Tomme
authors.forename: E
authors.initials: E
authors.lastname: Kwan
authors.forename: D G
authors.initials: DG
authors.lastname: Kilburn
authors.forename: R C
authors.initials: RC
authors.lastname: Miller
authors.forename: R A
authors.initials: RA
authors.lastname: Warren
authors.forename: N R
authors.initials: NR
authors.lastname: Gilkes
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D002480:Cellulase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D043366:Cellulose 1,4-beta-Cellobiosidase; D006026:Glycoside Hydrolases / Q000378:metabolism*; D006868:Hydrolysis; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides; D017384:Sequence Deletion; D017386:Sequence Homology, Amino Acid
chemical_list: D009838:Oligodeoxyribonucleotides; D006026:Glycoside Hydrolases; D002480:Cellulase; D043366:Cellulose 1,4-beta-Cellobiosidase