tailieunhanh - Báo cáo khoa học: An investigation of the substrate specificity of the xyloglucanase Cel74A from Hypocrea jecorina

The substrate specificity of the xyloglucanase Cel74A fromHypocrea jeco-rina (Trichoderma reesei) was examined using several polysaccharides and oligosaccharides. Our results revealed that xyloglucan chains are hydro-lyzed at substituted Glc residues, in contrast to the action of all known xyloglucan endoglucanases (EC ). | ễFEBS Journal An investigation of the substrate specificity of the xyloglucanase Cel74A from Hypocrea jecorina Tom Desmet1 Tineke Cantaert1 Peter Gualfetti2 Wim Nerinckx1 Laurie Gross2 Colin Mitchinson2 and Kathleen Piens1 1 Department of Biochemistry Physiology and Microbiology Faculty of Sciences Ghent University Belgium 2 Genencor InternationalInc. Palo Alto CA USA Keywords Cel74A glycoside hydrolase Hypocrea jecorina Trichoderma reesei xyloglucanase Correspondence T. Desmet Department of Biochemistry Physiology and Microbiology Faculty of Sciences Ghent University K. L. Ledeganckstraat 35 B-9000 Ghent Belgium Fax 32 9 264 5332 Tel 32 9 264 5272 E-mail Received 2 August 2006 revised 21 October 2006 accepted 9 November 2006 doi The substrate specificity of the xyloglucanase Cel74A from Hypocrea jeco-rina Trichoderma reesei was examined using several polysaccharides and oligosaccharides. Our results revealed that xyloglucan chains are hydrolyzed at substituted Glc residues in contrast to the action of all known xyloglucan endoglucanases EC . The building block of xyloglucan XXXG where X is a substituted Glc residue and G is an unsubstituted Glc residue was rapidly degraded to XX and XG kcat s-1 and Km 120 pM at 37 C and pH 5 which has only been observed before with the oligoxyloglucan-reducing-end-specific cellobiohydrolase from Geotrichum EC . However the cellobiohydrolase can only release XG from XXXGXXXG whereas Cel74A hydrolyzed this substrate at both chain ends resulting in XGXX. Differences in the length of a specific loop at subsite 2 are discussed as being the basis for the divergent specificity of these xyloglucanases. The tropical soft rot fungus Hypocrea jecorina formerly Trichoderma reesei secretes one of the most efficient and best characterized mixtures of cellulolytic enzymes including at least five endoglucanases EG EC and two exoglucanases or cellobiohydro-lases CBH