Structural transformation of the peptide fragments from the reactive center loops of serpins: Circular dichroic studies

Two peptides, derived from the reactive center of ovalbumin.(OVARC) and pla sminogen activator inhibitor-1 (PAIRC) respectively were chemically synthes ized and investigated by circular dichroic spectroscopy. The secondary stru ctural transformation in solution and in solid state was studied. OVARC sho ws a nascent helical structure in aqueous solution, and its helical content increases under acidic conditions. There is no obvious structural conversi on from solution to solid state. PAIRC, however, undergoes a structural tra nsformation from random coil in aqueous solution to a typical beta -sheet s tructure in the solid state. Hexafluoroispropanol (HFIP) prompts helical st ructures of the two peptides in solution, but It seems to trigger the struc tural formation of beta -sheets in solid state. The novel structural transf ormation from random coil or nascent helical structure in aqueous solution to the alpha -helix in IMP and to the beta -sheet structure in solid state may reflect the conformational polymorphism of the serpin reactive centers and is implicated in the structural features of the amyloid aggregates.