tailieunhanh - Báo cáo khoa học: Characterization and mode of action of an exopolygalacturonase from the hyperthermophilic bacterium Thermotoga maritima

An intracellular pectinolytic enzyme, PelB (TM0437), from the hyperther-mophilic bacteriumThermotoga maritimawas functionally produced in Escherichia coliand purified to homogeneity. PelB belongs to family 28 of the glycoside hydrolases, consisting of pectin-hydrolysing enzymes. As one of the few bacterial exopolygalacturonases, it is able to remove monogalac-turonate units from the nonreducing end of polygalacturonate. | iFEBS Journal Characterization and mode of action of an exopolygalacturonase from the hyperthermophilic bacterium Thermotoga maritima Leon D. Kluskens1 Gert-Jan . van Alebeek2 Jasper Walther1 Alphons . Voragen2 Willem M. de Vos1 and John van der Oost1 1 Laboratory of Microbiology Wageningen University the Netherlands 2 Laboratory of Food Chemistry Wageningen University the Netherlands Keywords exopolygalacturonase hydrolytic mode of action pectin thermostable Correspondence J. van der Oost Laboratory of Microbiology Wageningen University Hesselink van Suchtelenweg 4 6703 CT Wageningen the Netherlands Fax 31 317 483829 Tel 31 317 483108 E-mail Received 28 July 2005 accepted 24 August 2005 doi An intracellular pectinolytic enzyme PelB TM0437 from the hyperther-mophilic bacterium Thermotoga maritima was functionally produced in Escherichia coli and purified to homogeneity. PelB belongs to family 28 of the glycoside hydrolases consisting of pectin-hydrolysing enzymes. As one of the few bacterial exopolygalacturonases it is able to remove monogalacturonate units from the nonreducing end of polygalacturonate. Detailed characterization of the enzyme showed that PelB is highly thermo-active and thermostable with a melting temperature of 105 C and a temperature optimum of 80 C the highest described to date for hydrolytic pectinases. PelB showed increasing activity on oligosaccharides with an increasing degree of polymerization. The highest activity was found on the pentamer 1000 U-mg-1 . In addition the affinity increased in conjunction with the length of the oligoGalpA chain. PelB displayed specificity for saturated oligoGalpA and was unable to degrade unsaturated or methyl-esterified oligoGalpA. Analogous to the exopolygalacturonase from Aspergillus tubingensis it showed low activity with xylogalacturonan. Calculations on the subsite affinity revealed the presence of four subsites and a high affinity for GalpA