CONFORMATION OF THERMALLY DENATURED RNASE T1 WITH INTACT DISULFIDE BONDS - A SMALL STUDY BY SMALL-ANGLE X-RAY-SCATTERING

Small-angle X-ray scattering of RNase Tl with intact disulfide bonds w as measured at 20 degrees and 60 degrees C in order to get insight int o the structural changes of the protein caused by thermal denaturation . The radius of gyration increases from R-G - 1.43 nm to R-G = 2.21 nm . The conformations of the molecules at 60 degrees C are similar to th ose of ring-shaped random walk chains. However, the molecules are more compact than one would expect under theta conditions due to attractiv e interactions between the chain segments. The volume needed for free rotation of the thermally unfolded protein molecules about any axis in solution is five times greater than in the native state whereas the h ydrodynamic effective volume is increasing only two times. (C) 1997 El sevier Science B.V.