Enhancement of the Endo-β-1,4-glucanase Activity of an Exocellobiohydrolase by Deletion of a Surface Loop (∗)

• Published in: The Journal of biological chemistry 1995-03, Vol.270 (9), p.4383-4386
• Main Authors: Meinke, Andreas, Damude, Howard G., Tomme, Peter, Kwan, Emily, Kilburn, Douglas G., Miller, Robert C., Warren, R.Antony J., Gilkes, Neil R.
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; amino acid sequences; Base Sequence; binding sites; Cellulase - chemistry; Cellulase - genetics; Cellulase - metabolism; Cellulomonas; cellulose; Cellulose 1,4-beta-Cellobiosidase; deletions; enzyme activity; Glycoside Hydrolases - metabolism; Hydrolysis; kinetics; Molecular Sequence Data; O-glycoside hydrolases; Oligodeoxyribonucleotides; oligosaccharides; plasmid vectors; Sequence Deletion; Sequence Homology, Amino Acid; site-directed mutagenesis; substrates; Trichoderma reesei
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.270.9.4383

In the commonly accepted mechanism for enzymatic hydrolysis of cellulose, endo-β-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-β-D-cellobioside, insoluble cellulose, and cellotetraose.