Folding of SNase R begins early during synthesis: the conformational feature of two short N-terminal fragments of staphylococcal nuclease R.

ABSTRACT

To further understand the folding of nascent peptide during the early course of peptide synthesis, two short N-terminal fragments of staphylococcal nuclease R (SNase R), SNR52 and SNR79, were made by deleting 97 and 70 amino acid residues from the C-terminus. The conformations of SNR52 and SNR79 were studied by FTIR and far-ultraviolet CD. The results demonstrate that even the short N-terminal fragments of SNase R still have a certain amount of residual ordered secondary structure in the physiological condition. The ordered secondary structures were mainly assigned as beta-strands and turns, which corresponds well to the structures of the N-terminal part in the native protein. The conformational changes during unfolding and refolding in different concentrations of guanidine hydrochloride (GuHCl), monitored by far-ultraviolet CD and intrinsic fluorescence, show that the interaction between amino acid residues, which governs the formation of their conformation are not random. Considered together with earlier studies (Jing et al., Biochim Biophys Acta 1995;1250189-196; Zhou et al., J Biochem 1996120 881-888), the results suggest that the folding of nascent peptide chains begins early in the synthesis process and that the amount of ordered structure increases with increasing peptide chain length until the conformation of the biologically active protein is generated.