title: Purification and characterization of beta 2-tomatinase, an enzyme involved in the degradation of alpha-tomatine and isolation of the gene encoding beta 2-tomatinase from Septoria lycopersici.
abstract: Lycopersicon species often contain the toxic glycoalkaloid alpha-tomatine, which is proposed to protect these plants from general microbial infection. however, fungal pathogens of tomato often are tolerant to alpha-tomatine and detoxification of alpha-tomatine may be how these pathogens avoid this potential barrier. As an initial step to evaluate this possibility, we have purfied to homogeneity a beta-1,2-D glucosidase from the tomato pathogen Septoria lycopersici that hydrolyzes the beta-1,2-D glucosyl bond on the tetrasaccharide moiety of alpha-tomatine to produce beta2-tomatine. The enzyme is a 110-kDa protein with a pI of 4.5 and a Km for alpha-tomatine of 62 microM. Little or no activity was detected on a variety of other glycosides. The gene encoding this protein was isolated and contains an open reading frame of 803 amino acids that shares sequence homology with several other beta-D-glucosidases. When S. lycopersici was incubated with alpha-tomatine, beta2-tomatinase mRNA accumulated, suggesting that the enzyme is substrate inducible. Aspergillus nidulans expressed ¿beta2-tomatinase¿ activity when transformed with this gene but transformants were still sensitive to alpha-tomatine.
authors.affiliation: Department of Plant Pathology, University of Arizona, Tucson 85721, USA.
authors.forename: R W
authors.initials: RW
authors.lastname: Sandrock
authors.forename: D
authors.initials: D
authors.lastname: DellaPenna
authors.forename: H D
authors.initials: HD
authors.lastname: VanEtten
mesh_terms: D000595:Amino Acid Sequence; D001233:Aspergillus nidulans / Q000187:drug effects / Q000235:genetics; D001483:Base Sequence; D004305:Dose-Response Relationship, Drug; D004352:Drug Resistance, Microbial; D004790:Enzyme Induction; D015966:Gene Expression Regulation, Fungal; D005800:Genes, Fungal; D018551:Solanum lycopersicum / Q000382:microbiology; D003904:Mitosporic Fungi / Q000187:drug effects / Q000201:enzymology / Q000235:genetics*; D008969:Molecular Sequence Data; D017421:Sequence Analysis; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D014053:Tomatine / Q000378:metabolism* / Q000494:pharmacology; D014170:Transformation, Genetic; D001617:beta-Glucosidase / Q000737:chemistry / Q000235:genetics* / Q000302:isolation & purification
chemical_list: D014053:Tomatine; D001617:beta-Glucosidase