STRUCTURAL DISSECTION OF THE MULTIDOMAIN KININOGENS - FINE MAPPING OFTHE TARGET EPITOPES OF ANTIBODIES INTERFERING WITH THEIR FUNCTIONAL-PROPERTIES

Kininogens, the large precursor molecules of the vasoactive kinin pept ides, are prototypic multidomain proteins serving numerous functions. To investigate their structure-function relationships, we have raised a panel of monoclonal antibodies against human H-kininogen and L-kinin ogen and fragments thereof and characterized them with respect to thei r target epitopes. Of 35 antibodies, 12 were directed to the aminoterm inal domains (D1 to D3) of cystatin-like structure, 3 recognized domai n D4 bearing the kinin segment, 17 bound to the carboxyl-terminal doma ins of H-kininogen (D5H and D6H), and 3 bound to the carboxyl-terminal domain D5L of L-kininogen. At least 14 distinct epitopes spread over the kininogen molecules were identified: 9 epitopes located on L-kinin ogen and 13 epitopes harbored by H-kininogen. Of these, 8 are shared b y the two types of kininogens. Fine mapping of the epitopes by proteol ytic fragments, recombinant proteins, and anti-idiotypic antibodies de monstrated that most but not all of the antibodies recognize linear ep itopes. Synthesis of 28 peptides covering more than one-third of the e ntire kininogen sequences allowed us to narrow down seven major epitop es to 7-31 residues. Functional analyses identified 14 antibodies inte rfering with specific biological roles of the kininogens, i.e. cystein e proteinase inhibition, platelet attachment, cofactor binding, contac t activation, and kinin delivery. Cross-reactivity studies indicated t hat three of the epitopes are present throughout the mammalian kininog ens and further identified a unique epitope characteristic for the H/L -type of kininogens not present in their T-type. The panel of mapped a ntibodies provides powerful tools for the characterization of relevant interaction sites exposed by the pleiotropic kininogens and for the d evelopment of molecular surrogates mimicking these functional loci.