PHYSICAL AND BIOLOGICAL SIGNIFICANCE OF PEPTIDE SEQUENCES MEDIATING THE INTERACTION BETWEEN HIGH-MOLECULAR-WEIGHT KININOGEN AND PLASMA PREKALLIKREIN

HK31 (S565-K595) has previously been shown to encompass the binding do main for plasma prekallikrein (PK) within domain 6 of high molecular w eight kininogen (HK). The complementary binding domain for HK within P K is mapped to PK56 (F56-G86), in the Apple 1 domain and to PK266 (K26 6-C295) in the Apple 4 domain. Isothermal titration calorimetry demons trated that either PK peptide binds to HK31 in 1:1 stoichiometry. Bind ing of the alternate PK peptide into a ternary complex is facilitated nearly 2-fold, Fluorescence emission spectroscopy revealed that only t he binding of PK56 caused a limited decrease in intrinsic tryptophane fluorescence emission intensity of HK31. We conclude that the two PK p eptides bind to the HK peptide at different sites. To map the minimal sequence within HK31, truncated new peptides were tested for their abi lity to compete with HK for binding PK in a cell-free system. D567-T59 1, a 25-residue peptide which contains sufficient structural informati on for binding kallikrein in solution, blocked the binding of kallikre in to HK bound to endothelial cells and inhibited PK activation to kal likrein and the generation of kallikrein-activated urokinase on endoth elial cell surfaces. HK-derived peptides could modulate excessive fibr inolysis and hypotension in sepsis and multiple trauma.