title: An extracellular exo-beta-(1,3)-glucanase from Pichia pastoris: purification, characterization, molecular cloning, and functional expression.
abstract: An extracellular exo-beta-(1,3)-glucanase (designated EXG1) was purified to apparent homogeneity from Pichia pastoris X-33 cultures by ammonium sulfate fractionation, ion-exchange chromatography, and gel filtration. The native enzyme is unglycosylated and monomeric with a molecular mass of approximately 47kDa. At its optimal pH of 6.0, the enzyme shows highest activity among physiological substrates toward laminarin (apparent Km, 3.5 mg/ml; Vmax, 192 micromole glucose produced/min/mg protein) but also hydrolyzes amygdalin and esculin, and the chromogenic substrates p-nitrophenyl-beta-D-glucopyranoside and p-nitrophenyl-beta-D-xylopyranoside. The P. pastoris EXG1 gene was cloned by a PCR-based strategy using genomic DNA as template. This intronless gene predicts an ORF that encodes a primary translation product of 414 amino acids. We believe that this preproprotein is processed sequentially by signal peptidase and a Kex2-like endoprotease to yield a mature protein of 392 amino acids (45,376 Da; pI, 4.46) that shares 36-64% amino acid identity with other yeast exo-beta-(1,3)-glucanases belonging to Glycoside Hydrolase Family 5. It also possesses the eight invariant residues and signature pattern [LIV]-[LIVMFYWGA](2)-[DNEQG]-[LIVMGST]-X-N-E-[PV]-[RHDNSTLIVFY] shown by all Family 5 members. Overexpression of the cloned EXG1 gene in Pichia cells, followed by Ni-CAM HC resin chromatography, yielded milligram quantities of homogeneous recombinant EXG1 in active form for further characterization studies.
authors.affiliation: Department of Biological Sciences, University of Iowa, Iowa City, IA 52242, USA.
authors.forename: Zhiwei
authors.initials: Z
authors.lastname: Xu
authors.forename: Ming-Che
authors.initials: MC
authors.lastname: Shih
authors.forename: Jonathan E
authors.initials: JE
authors.lastname: Poulton
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D005110:Extracellular Space / Q000201:enzymology* / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D043326:Glucan 1,3-beta-Glucosidase / Q000737:chemistry / Q000235:genetics* / Q000302:isolation & purification* / Q000502:physiology; D008969:Molecular Sequence Data; D010843:Pichia / Q000201:enzymology* / Q000235:genetics; D016415:Sequence Alignment
chemical_list: D043326:Glucan 1,3-beta-Glucosidase