TRIFLUOROETHANOL-INDUCED CONFORMATIONAL TRANSITION OF HEN EGG-WHITE LYSOZYME STUDIED BY SMALL-ANGLE X-RAY-SCATTERING

The trifluoroethanal (TFE)-induced conformational transition of hen ly sozyme was studied with the combined use of far-UV circular dichroism (CD) and small-angle X-ray scattering, At pH 2.0 and 20 degrees C, the addition of TFE to the native lysozyme induced a cooperative transiti on to an intermediate state with an increased helical content (TFE sta te), Small-angle X-ray scattering measurements indicated that the TFE state has a radius of gyration which is 20% larger than that of the na tive state and assumes a chain-like conformation with some remaining g lobularity. The TFE-induced transition curves obtained by CD and the s mall-angle X-ray scattering measurements agreed well, consistent with a two-state transition mechanism. A singular value decomposition analy sis of Kratky plots of the small-angle X-ray scattering profiles indic ated that two basic scattering functions reproduce the observed spectr a, further confirming the validity of a two-state approximation. (C) 1 997 Federation of European Biochemical Societies.