AMINOTHIOTYROSINE DISULFIDE, AN OPTICAL TRIGGER FOR INITIATION OF PROTEIN-FOLDING

The development of an optical trigger for protein folding is described . The optical trigger is an aryl disulfide embedded in a polypeptide s uch that the aryl disulfide constrains the peptide in a nonhelical con formation. Upon photocleavage of the SS bond, the peptide can then com mence to fold into an a-helical conformation. Two thiotyrosine derivat ives, (S)-4'-mercaptophenylalanine (Tty) and 3-N-(4'-mercaptophenyl)-( S)-2,3-diaminoproprionate (Aty), have been prepared and incorporated i nto polyalanine peptides. The ease of synthesis of protected forms of Tty and Aty amenable for solid phase synthesis, in four steps with 30% overall yield and six steps in 40% overall yield, respectively, make these attractive candidates as precursors of the optical trigger. CD a nd IR spectroscopy showed that the cyclic disulfide cross-linked pepti des are much less helical than their linear counterparts. Following la ser flash photolysis, peptide 7, which incorporates Tty, showed total recombination of the thiyl radicals within 1 ns. Peptide 16, which inc orporates Aty, showed a significant amount of long-lived thiyl radical s from nanosecond to microsecond time scale. The process of recombinat ion is hypothesized to be governed by the peptide conformation. Becaus e of the significant amount of long-lived thiyl radicals generated fro m cyclic peptide 16, Aty should prove to be of general utility in the studies of protein folding on a time scale of sub-picoseconds and grea ter.