Structural Insights into the β-Xylosidase from Trichoderma reesei Obtained by Synchrotron Small-Angle X-ray Scattering and Circular Dichroism Spectroscopy

• Published in: Biochemistry (Easton) 2005-11, Vol.44 (47), p.15578-15584
• Main Authors: Rojas, Adriana L., Fischer, Hannes, Eneiskaya, Elena V., Kulminskaya, Anna A., Shabalin, Konstantin A., Neustroev, Kirill N., Craievich, Aldo F., Golubev, Alexander M., Polikarpov, Igor
• Format: Article
• Language: English
• Subjects: Algorithms; Circular Dichroism; Models, Molecular; Protein Conformation; Protein Structure, Secondary; Scattering, Radiation; Solutions; Trichoderma - enzymology; X-Rays; Xylosidases - chemistry
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi050826j

The enzyme β-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-β-xylooligosaccharides and that also exhibits α-l-arabinofuranosidase activity on 4-nitrophenyl α-l-arabinofuranoside. In this work, we show that the enzyme forms monomers in solution and derive the low-resolution molecular envelope of the β-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 β-xylosidase are 30.3 ± 0.2 and 90 ± 5 Å, respectively. In contrast to the fold of the only two structurally characterized members of GH3, the barley β-d-glucan exohydrolase and β-hexosaminidase from Vibrio cholerae, which have respectively two or one distinct domains, the shape of the β-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 β conformation.