STRUCTURAL CONTRIBUTION OF THE A-CHAIN LOOP IN RELAXIN

Site-directed sequential disulfide bond formation has been used to syn thesize relaxin analogs with modifications in the A chain loop (A10-A1 5). In the four different derivatives either the amino acid residues b etween the cysteines (A12-A14) were replaced or the intrachain disulfi de bond (A10-A15) was eliminated. The substitution of the human relaxi n II sequence (His-Val-Gly; A12-14) by the corresponding insulin seque nce (Thr-Ser-Ile) or the hydrocarbon chain of omega-aminooctanoic acid (Aoc) caused significant loss of biological activity. Similar observa tions were made when the pair of cysteines (A10-A15) was replaced by e ither alanine or serine, whereby serine disturbs more than alanine. It is suggested that the structural features of the A chain loop not onl y make important contributions to the active conformation of relaxin b ut also that the structural requirements of insulin and relaxin are di fferent. (C) Munksgaard 1995.