[Hydrogen exchange and the proteolytic degradation of ribonuclease A. The position of the centers of the high-temperature splitting by proteases and the structure of denatured molecules].

The information on the high-temperature proteolytic degradation of RNase A has been analyzed. It has been shown that a few peptide bonds primarily splitted by trypsin, chymotrypsin and thermolysin are localized only in the N-terminal part of structural domain II of the native molecule. The same peptide bonds are splitted by proteases with the highest rate upon the denaturation in the presense of trifluoroethanol or the renaturation from concentrated urea solutions and after the desorganization of the native structure by the reduction of all four S-S bonds of RNase A. According to the data on hydrogen exchange in the native RNase A molecule, the dynamic stability of the tertiary structure of domain II is lower than that of domain I because of the lesser amount of the internal bulky nonpolar residues Val, Ile, and Phe. For the same reason, this part of the molecule in different nonnative forms of RNase A is less compact and more flexible and is splitted with the highest rate in the segment 31-39 enriched by long cationic residues Lys and Arg. A common feature of the conformation of the flexible disordered backbone of all RNase A nonnative structures considered is the predominance of short PPII helices, which provides a high rate of the restoration of the native secondary and tertiary structures upon renaturation or self-organization and global fluctuations of the native structure revealed by the hydrogen exchange and proteolytic degradation.