Conformational properties of the N‐terminal residues of S‐peptide. I. The ribonuclease S′ system

Abstract

AbstractThe contribution of the 1–6 N‐terminal sequence to the conformational properties of the S‐peptide (the 1–20 sequence of ribonuclease A) was assessed by determining in the ribonuclease S′ system the helical content and the binding capability of synthetic [Orn10]‐S‐peptide analogs, in which lysine1, glutamic2 and threonine3 were progressively deleted, alanine4 and alanine5were alternatively replaced by serine, and alanine6 was substituted by serine or proline. Both the deletion of the three N‐terminal residues and the alanine6/proline replacement produces the loss of the helical structure up to lysine7. No or minor effects are found in all other cases. From the comparison of the binding data, the energy for the conformational stabilization of the N‐terminal region was calculated to amount to 1.4 kcal/mol. The results are discussed in comparison with the known x‐ray data of the enzyme, with some predictive rules of secondary structure which were applied to this region and with the known phylogenetic variance of the residues in this region.