THERMODYNAMIC STABILITY OF 2 VARIANTS OF XYLANASE (XYS1) FROM STREPTOMYCES-HALSTEDII JM8

In a continuation of our earlier study [Ruiz-Arribas, A., Santamaria, R.I., Zhadan, G.G., Villar, E. & Shnyrov, V.L. (1994) Differential sca nning calorimetric study of the thermal stability of xylanase from Str eptomyces halstedii JM8, Biochemistry 33, 13787-13791], we used high-s ensitivity differential scanning microcalorimetry, intrinsic tryptopha n fluorescence and far-ultraviolet circular dichroism to study the eff ect of regional sequence differences on the thermodynamic stability of xylanase (Xys1) from Streptomyces halstedii JM8 (1,4-beta-D-xylanohyd rolase, EC 3.2.1.8). Thermal transitions were measured for original xy lanase (Xys1S) and two variants. Thermal denaturation of all the xylan ases studied revealed two structural domains, each of which, despite i ts partial irreversibility, follows a two-state thermal unfolding proc ess under our experimental conditions. Both variants were found to exh ibit slightly decreased stability, possessing the same activity as the original. The unfolding parameters for each domain of both variants, unlike the situation with wild-type xylanase (see our previous report) , fit some correlations obtained for the most compact globular protein s. The values of enthalpy and entropy of unfolding/residue at 383 K we re found to be inversely proportional to residual, well-regulated stru ctures in unfolded states.