title: Exo-mode of action of cellobiohydrolase Cel48C from Paenibacillus sp. BP-23. A unique type of cellulase among Bacillales.
abstract: Sequence analysis of a Paenibacillus sp. BP-23 recombinant clone coding for a previously described endoglucanase revealed the presence of an additional truncated ORF with homology to family 48 glycosyl hydrolases. The corresponding 3509-bp DNA fragment was isolated after gene walking and cloned in Escherichia coli Xl1-Blue for expression and purification. The encoded enzyme, a cellulase of 1091 amino acids with a deduced molecular mass of 118 kDa and a pI of 4.85, displayed a multidomain organization bearing a canonical family 48 catalytic domain, a bacterial type 3a cellulose-binding module, and a putative fibronectin-III domain. The cloned cellulase, unique among Bacillales and designated Cel48C, was purified through affinity chromatography using its ability to bind Avicel. Maximum activity was achieved at 45 degrees C and pH 6.0 on acid-swollen cellulose, bacterial microcrystalline cellulose, Avicel and cellodextrins, whereas no activity was found on carboxy methyl cellulose, cellobiose, cellotriose, pNP-glycosides or 4-methylumbeliferyl alpha-d-glucoside. Cellobiose was the major product of cellulose hydrolysis, identifying Cel48C as a processive cellobiohydrolase. Although no chromogenic activity was detected from pNP-glycosides, TLC analysis revealed the release of p-nitrophenyl-glycosides and cellodextrins from these substrates, suggesting that Cel48C acts from the reducing ends of the sugar chain. Presence of such a cellobiohydrolase in Paenibacillus sp. BP-23 would contribute to widen up its range of action on natural cellulosic substrates.
authors.affiliation: Department of Microbiology, Faculty of Biology, University of Barcelona, Spain.
authors.forename: Marta M
authors.initials: MM
authors.lastname: Sánchez
authors.forename: F I Javier
authors.initials: FI
authors.lastname: Pastor
authors.forename: Pilar
authors.initials: P
authors.lastname: Diaz
mesh_terms: D001407:Bacillus / Q000201:enzymology* / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002480:Cellulase / Q000235:genetics / Q000378:metabolism*; D002482:Cellulose / Q000378:metabolism; D043366:Cellulose 1,4-beta-Cellobiosidase; D016366:Open Reading Frames; D013379:Substrate Specificity
chemical_list: D001426:Bacterial Proteins; D002482:Cellulose; D002480:Cellulase; D043366:Cellulose 1,4-beta-Cellobiosidase