Identification and characterization of some Aspergillus pectinolytic glycoside hydrolases

J.S. Zandleven

Research output: Thesisinternal PhD, WU

Abstract

Keywords: Aspergillusniger , Arabidopsis thaliana , homogalacturonan, rhamnogalacturonan, xylogalacturonan, xylogalacturonan hydrolase, exo-polygalacturonasePectinases are used for many food applications, in particular for the manufacture of fruit juices. However, the array of pectin modifying enzymes as available today is insufficient to completely degrade pectic polysaccharides from plants, which consequently can cause problems in food processing. As the genome sequence of Aspergillusniger indicated the presence of more pectin modifying enzymes than previously known, research was carried out to identify, produce, and characterize novel pectinases from this species.From the complete inventory of the pectinolytic glycoside hydrolase family 28 of A.niger a new gene group of seven exo-acting enzymes was found. Three of these enzymes (PGXA, PGXB, PGXC) were biochemically identified from which it was demonstrated that PGXB and PGXC act as an exo-polygalacturonase while PGXA rather acts like an exo-xylogalacturonan hydrolase.The xylogalacturonan hydrolase (XGH) was thoroughly investigated for its action towards a xylogalacturonan (XGA) derived from gum tragacanth by isolation and characterization of the produced oligosaccharides. Also XGH activity towards XGA in the saponified modified 'hairy' regions (MHR-s) of pectin from apples and potatoes was investigated. The enzyme predominantly released the di-saccharide GalAXyl from these substrates which illustrates the preference of XGH to act between two xylosylated GalA residues. However this enzyme was also able to release low substituted XGA oligosaccharides as well as linear GalA oligosaccharides, which shows its tolerance for unsubstituted GalA residues in its active site.By using XGH as analytical tool, the presence of XGA could also be demonstrated in the stem and the leaves of Arabidopsis thaliana , which shows that the presence of this polymer is not strictly confined to storage tissues or reproductive organs of plants as was previously thought to be the case.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Wageningen University
Supervisors/Advisors
  • Voragen, Fons, Promotor
  • Beldman, Gerrit, Co-promotor
Award date12 Dec 2006
Place of Publication[S.l.]
Print ISBNs9789085045519
Publication statusPublished - 2006

Keywords

  • polygalacturonase
  • pectins
  • cell wall components
  • aspergillus niger
  • microbial degradation
  • arabidopsis thaliana

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