Synthesis, biological activity, and solution structures of a cyclic dodecapeptide from the EGF-2 domain of blood...

The cyclic dodecapeptide, disulfide-cyclo-[H-Cys-Val-Asn-Glu-Asn-Gly-Gly-Cys(Acm)-Glu-Gln-Tyr-Cys-OH], which corresponds to the 91-102 sequence of the second epidermal growth factor domain of human blood coagulation factor VII, was synthesized using solid-phase procedures. It was shown to be an inhibitor at the key step in the induction of coagulation by the extrinsic pathway, i.e. the factor VII/tissue factor-catalyzed activation of coagulation factor X. The solution structure of this peptide was investigated by NMR spectroscopy and was computer-modeled via molecular mechanics. Structures were calculated based on 112 distance and nine dihedral angle constraints. The resulting backbone structures were classified into two structural subsets: one which exhibited a twisted '8'-shaped folding and another describing an open, circular 'O' outline. The local backbone structures of segments Asn3-Glu4-Asn5, Gly7-Cys8 and Gln10-Tyr11 were well preserved among the two subsets. Apart from the unrestrained N- and C-termini, Gly6 and Glu9 sites exhibited marked local disorder between the two subsets, suggesting localized flexible hinges likely to govern tertiary structure interconversion between the two subsets. Two transient hydrogen bonds were identified from pH chemical shift titrations by matching the pKa values of NH and carboxylate groups, which supported the occurrence of the '8' structure, and agreed with temperature coefficients of peptidyl NH resonances. Structure-function relationships of the peptide were discussed in terms of the likely physiological function of the disulfide-bonded loop in factor VII which the peptide represents.