title: Structural insights into the beta-xylosidase from Trichoderma reesei obtained by synchrotron small-angle X-ray scattering and circular dichroism spectroscopy.
abstract: The enzyme beta-xylosidase from Trichoderma reesei, a member of glycosil hydrolase family 3 (GH3), is a glycoside hydrolase which acts at the glycosidic linkages of 1,4-beta-xylooligosaccharides and that also exhibits alpha-l-arabinofuranosidase activity on 4-nitrophenyl alpha-l-arabinofuranoside. In this work, we show that the enzyme forms monomers in solution and derive the low-resolution molecular envelope of the beta-xylosidase from small-angle X-ray scattering (SAXS) data using the ab initio simulated annealing algorithm. The radius of gyration and the maximum dimension of the beta-xylosidase are 30.3 +/- 0.2 and 90 +/- 5 A, respectively. In contrast to the fold of the only two structurally characterized members of GH3, the barley beta-d-glucan exohydrolase and beta-hexosaminidase from Vibrio cholerae, which have respectively two or one distinct domains, the shape of the beta-xylosidase indicates the presence of three distinct structural modules. Domain recognition algorithms were used to show that the C-terminal part of the amino acid sequence of the protein forms the third domain. Circular dichroism spectroscopy and secondary structure prediction programs demonstrate that this additional domain adopts a predominantly beta conformation.
authors.affiliation: Instituto de Física de São Carlos, Universidade de São Paulo, Av. Trabalhador São-carlense 400, CEP 13560-970, São Carlos, SP, Brazil.
authors.forename: Adriana L
authors.initials: AL
authors.lastname: Rojas
authors.forename: Hannes
authors.initials: H
authors.lastname: Fischer
authors.forename: Elena V
authors.initials: EV
authors.lastname: Eneiskaya
authors.forename: Anna A
authors.initials: AA
authors.lastname: Kulminskaya
authors.forename: Konstantin A
authors.initials: KA
authors.lastname: Shabalin
authors.forename: Kirill N
authors.initials: KN
authors.lastname: Neustroev
authors.forename: Aldo F
authors.initials: AF
authors.lastname: Craievich
authors.forename: Alexander M
authors.initials: AM
authors.lastname: Golubev
authors.forename: Igor
authors.initials: I
authors.lastname: Polikarpov
mesh_terms: D000465:Algorithms; D002942:Circular Dichroism; D008958:Models, Molecular; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D012542:Scattering, Radiation; D012996:Solutions; D014242:Trichoderma / Q000201:enzymology*; D014965:X-Rays; D014995:Xylosidases / Q000737:chemistry*
chemical_list: D012996:Solutions; D014995:Xylosidases; C026579:exo-1,4-beta-D-xylosidase