title: Degradation and synthesis of β-glucans by a Magnaporthe oryzae endotransglucosylase, a member of the glycoside hydrolase 7 family.
abstract: BACKGROUND
  Plant pathogens secrete enzymes that degrade plant cell walls to enhance infection and nutrient acquisition.
  
  
  RESULTS
  A novel endotransglucosylase catalyzes cleavage and transfer of β-glucans and decreases the physical strength of plant cell walls.
  
  
  CONCLUSIONS
  Endotransglucosylation causes depolymerization and polymerization of β-glucans, depending on substrate molecular size.
  
  
  CONCLUSIONS
  Enzymatic degradation of plant cell walls is required for wall loosening, which enhances pathogen invasion. A Magnaporthe oryzae enzyme, which was encoded by the Mocel7B gene, was predicted to act on 1,3-1,4-β-glucan degradation and transglycosylation reaction of cellotriose after partial purification from a culture filtrate of M. oryzae cells, followed by liquid chromatography-tandem mass spectrometry. A recombinant MoCel7B prepared by overexpression in M. oryzae exhibited endo-typical depolymerization of polysaccharides containing β-1,4-linkages, in which 1,3-1,4-β-glucan was the best substrate. When cellooligosaccharides were used as the substrate, the recombinant enzyme generated reaction products with both shorter and longer chain lengths than the substrate. In addition, incorporation of glucose and various oligosaccharides including sulforhodamine-conjugated cellobiose, laminarioligosaccharides, gentiobiose, xylobiose, mannobiose, and xyloglucan nonasaccharide into β-1,4-linked glucans were observed after incubation with the enzyme. These results indicate that the recombinant enzyme acts as an endotransglucosylase (ETG) that cleaves the glycosidic bond of β-1,4-glucan as a donor substrate and transfers the cleaved glucan chain to another molecule functioning as an acceptor substrate. Furthermore, ETG treatment caused greater extension of heat-treated wheat coleoptiles. The result suggests that ETG functions to induce wall loosening by cleaving the 1,3-1,4-β-glucan tethers of plant cell walls. On the other hand, use of cellohexaose as a substrate for ETG resulted in the production of cellulose II with a maximum length (degree of polymerization) of 26 glucose units. Thus, ETG functions to depolymerize and polymerize β-glucans, depending on the size of the acceptor substrate.
authors.affiliation: Iwate Biotechnology Research Center, 22-174-4, Narita Kitakami, Iwate 024-0003, Japan.
authors.forename: Machiko
authors.initials: M
authors.lastname: Takahashi
authors.forename: Koichi
authors.initials: K
authors.lastname: Yoshioka
authors.forename: Tomoya
authors.initials: T
authors.lastname: Imai
authors.forename: Yuka
authors.initials: Y
authors.lastname: Miyoshi
authors.forename: Yuki
authors.initials: Y
authors.lastname: Nakano
authors.forename: Kentaro
authors.initials: K
authors.lastname: Yoshida
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Yamashita
authors.forename: Yuzo
authors.initials: Y
authors.lastname: Furuta
authors.forename: Takashi
authors.initials: T
authors.lastname: Watanabe
authors.forename: Junji
authors.initials: J
authors.lastname: Sugiyama
authors.forename: Takumi
authors.initials: T
authors.lastname: Takeda
mesh_terms: D002236:Carbohydrate Conformation; D002473:Cell Wall / Q000737:chemistry; D002482:Cellulose / Q000096:biosynthesis; D003001:Cloning, Molecular; D018548:Cotyledon / Q000737:chemistry / Q000166:cytology; D005656:Fungal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006026:Glycoside Hydrolases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006868:Hydrolysis; D020082:Magnaporthe / Q000201:enzymology*; D009844:Oligosaccharides / Q000737:chemistry; D012275:Oryza / Q000382:microbiology; D018515:Plant Leaves / Q000382:microbiology; D013379:Substrate Specificity; D014158:Transcription, Genetic; D014908:Triticum / Q000737:chemistry / Q000166:cytology; D047071:beta-Glucans / Q000378:metabolism*
chemical_list: D005656:Fungal Proteins; D009844:Oligosaccharides; D047071:beta-Glucans; D002482:Cellulose; D006026:Glycoside Hydrolases
keywords: Cell Wall; Cell Wall-degrading Enzymes; Cellulase; Enzyme Purification; Enzymes; Glycobiology