The family 52 β-xylosidase from Geobacillus stearothermophilus is a dimer: Structural and biophysical characterization of a glycoside hydrolase
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Contreras Moyeja, Lellys Mariela; Gomez, J; Prieto, J; Clemente Jiménez, Josefa María; Las Heras Vázquez, Francisco Javier; [et al.]Date
2008Abstract
Xylans are the most abundant polysaccharides forming the plant cell wall hemicelluloses, and they are
degraded, among other proteins, by β-xylosidase enzymes. In this work, the structural and biophysical
properties of the family 52 β-xylosidase from Geobacillus stearothermophilus, XynB2, are described. Size
exclusion chromatography, analytical centrifugation, ITC, CD, fluorescence (steady state and ANS-binding)
and FTIR were used to obtain the structure, the oligomerization state and the conformational changes of
XynB2, as pH, chemical denaturants or temperature were modified. This report describes the first extensive
conformational characterization of a family 52 β-xylosidase. The active protein was a highly hydrated dimer,
whose active site was formed by the two protomers, and it probably involved aromatic residues. At low pH,
the protein was not active and it populated a monomeric molten-globule-like species, which had a
conformational transition with a pKa of ~4.0. Thermal...
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Conformation
FTIR
Molten globule
Fluorescence
Circular dichroism
Structure