Conformation of thermally denatured RNase T1 with intact disulfide bonds: a study by small-angle X-ray scattering.

Small-angle X-ray scattering of RNase T1 with intact disulfide bonds was measured at 20 degrees and 60 degrees C in order to get insight into 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 those of ring-shaped random walk chains. However, the molecules are more compact than one would expect under theta conditions due to attractive 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 hydrodynamic effective volume is increasing only two times.