COMPARATIVE-STUDIES OF THE CONFORMATION OF THE N-TERMINAL FRAGMENTS OF STAPHYLOCOCCAL NUCLEASE-R IN SOLUTION

In order to elucidate the folding of nascent peptide, five peptide fra gments of staphylococcal nuclease R starting from N-terminal end and o f different chain lengths are made by deletion of 47, 39, 28, 14 and 8 amino-acid residues from its C-terminal end, respectively. Changes in conformation of the N-terminal fragments have been compared by using Fourier-transform infrared spectra, far-ultraviolet circular dichroism spectra and analysis of surface hydrophobicity. The experiments indic ate that all the five fragments have certain amounts of residual struc ture; in general, with increasing the peptide chain, the contents of s econdary structure and the enzyme's activity of the peptide increase, and the exposed hydrophobic side chains brought about by the deletion of C-terminal residues are gradually buried in the interior of the nuc lease. However, the ordered secondary structures do not always increas e with increasing the peptide chain, further growth of the length of t he peptide chain could have an important effect on the conformation of the peptide fragment already synthesized, suggesting some structural adjustments should be necessary in order for the newly synthesized pol ypeptide to attain its final native conformation. These results suppor t Tsou's nascent peptide folding hypothesis (Tsou, C.-L. (1988) Bioche mistry 27, 1809-1812).