FOLDING OF SNASE-R BEGINS EARLY DURING SYNTHESIS - THE CONFORMATIONALFEATURE OF 2 SHORT N-TERMINAL FRAGMENTS OF STAPHYLOCOCCAL NUCLEASE-R

To further understand the folding of nascent peptide during the early course of peptide synthesis, two short N-terminal fragments of staphyl ococcal nuclease R (SNase R), SNR52 and SNR79, were made by deleting 9 7 and 70 amino acid residues from the C-terminus. The conformations of SNR52 and SNR79 were studied by FTIR and far-ultraviolet CD. The resu lts demonstrate that even the short N-terminal fragments of SNase R st ill have a certain amount of residual ordered secondary structure in t he physiological condition. The ordered secondary structures were main ly assigned as P-strands and turns, which corresponds well to the stru ctures of the N-terminal part in the native protein. The conformationa l changes during unfolding and refolding in different concentrations o f 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 ra ndom. Considered together with earlier studies (Jing et al., Biochim B iophys Acta 1995;1250:189-196; Zhou et al., J Biochem 1996,120: 881-88 8), the results suggest that the folding of nascent peptide chains beg ins early in the synthesis process and that the amount of ordered stru cture increases with increasing peptide chain length until the conform ation of the biologically active protein is generated. (C) 1998 Elsevi er Science B.V. All rights reserved.