Structural dissection of the multidomain kininogens. Fine mapping of the target epitopes of antibodies interfering with their functional properties.

Kininogens, the large precursor molecules of the vasoactive kinin peptides, 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-kininogen and fragments thereof and characterized them with respect to their target epitopes. Of 35 antibodies, 12 were directed to the amino-terminal domains (D1 to D3) of cystatin-like structure, 3 recognized domain D4 bearing the kinin segment, 17 bound to the carboxyl-terminal domains 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-kininogen and 13 epitopes harbored by H-kininogen. Of these, 8 are shared by the two types of kininogens. Fine mapping of the epitopes by proteolytic fragments, recombinant proteins, and anti-idiotypic antibodies demonstrated that most but not all of the antibodies recognize liner epitopes. Synthesis of 28 peptides covering more than one-third of the entire kininogen sequences allowed us to narrow down seven major epitopes to 7-31 residues. Functional analyses identified 14 antibodies interfering with specific biological roles of the kininogens, i.e. cysteine proteinase inhibition, platelet attachment, cofactor binding, contact activation, and kinin delivery. Cross-reactivity studies indicated that three of the epitopes are present throughout the mammalian kininogens and further identified a unique epitope characteristic for the H/L-type of kininogens not present in their T-type. The panel of mapped antibodies provides powerful tools for the characterization of relevant interaction sites exposed by the pleiotropic kininogens and for the development of molecular surrogates mimicking these functional loci.