FOURIER-TRANSFORM INFRARED (FT-IR) SPECTROSCOPIC STUDIES OF PEPTIDE MODELS FOR INTERACTION OF THE BINDING REGIONS OF HIGH-MOLECULAR-WEIGHT KININOGEN AND PREKALLIKREIN

The binding sites for high molecular weight kininogen (HK) on prekalli krein (PK) are composed of two discontinuous segments in the primary s equence, one in Apple 1 domain (PK56=F56-G86) and the other in Apple 4 (PK266=K266-G295). The site on HK, HK31, is subsumed in a 31-amino-ac id sequence (S565-K595) near the C-terminus which has the same affinit y for prekallikrein as the entire HK molecule. The binding among them is likely due to conformational changes which serve to juxtapose the P K binding domain within HK with the HK binding site. Resolution-enhanc ed Fourier transform infrared spectroscopy (FT-IR) has been employed t o analyze the contents of secondary structural elements of PK56 and HK 31 and to reveal the possible specific binding portion and structural changes in HK31 and PK56 upon binding. From the amide I bands of their deconvoluted FT-IR spectra, it is known that PK56 contains no helix c omponent, while HK31 has two different helical conformations. A quanti tative comparison of the spectra of HK31, PK56 and their binding compl ex suggests that the conformation of 3(10)-helix in HK31 has been chan ged to an alpha-helix, and one disordered segment of PK56 may have bee n changed to extended conformation. The other structural components in PK56 and HK31 remain unchanged. Since previous studies have shown tha t these peptides mimic the natural protein in their bioactivity, their interaction may reflect similar changes in the natural molecules. (C) 1998 Elsevier Science Ltd.