Structural changes enhance the activity of Chainia xylanase in low urea concentrations

• Published in: Biochimica et biophysica acta Vol. 1645; no. 2; pp. 164 - 171
• Main Authors: Kumar, Ameeta R, Hegde, Subray S, Ganesh, K.N, Khan, M.I
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 21.02.2003
• Subjects: Acrylamide; Actinomyces - enzymology; Circular Dichroism; Enzyme Activation - drug effects; Guanidine - pharmacology; Hydrogen-Ion Concentration; Protein Conformation - drug effects; Spectrometry, Fluorescence; Structure; Thermodynamics; Urea; Urea - pharmacology; Xylan Endo-1,3-beta-Xylosidase; Xylanase; Xylosidases - chemistry; Xylosidases - metabolism; Xylanase; Structure; Urea
• ISSN: 1570-9639; 0006-3002; 1878-1454; 1878-2434
• DOI: 10.1016/S1570-9639(02)00530-7

Low concentrations of urea (1.2 M) stimulated the activity of endo-xylanase from Chainia by 30%. Subtle structural changes in the monomeric protein were reflected in the secondary and tertiary structure of the enzyme as monitored by fluorescence and circular dichroism. Changes in λ max of emission, the fluorescence intensity and the Stern–Volmer quenching constants for acrylamide, measured in the presence of urea, indicated changes in the microenvironment of the Trp residues, suggesting alterations in tertiary structure. The ellipticity changes at 220 nm and Selcon analysis reflected changes in the content of β-sheet while both the near- and far-UV CD spectra indicated alterations in the secondary and tertiary structure of the protein in presence of urea. The dissociation constant values ( K d) show very little change in the affinity of the enzyme for the substrate while the k cat values suggest enhanced turnover of the substrate in presence of urea. We suggest that low urea concentrations perturb the conformational state of xylanase leading to an open and a more flexible structure, resulting in enhanced catalytic rates.