Disulphide-bond pattern and molecular modelling of the dimeric disintegrinEMF-10, a potent and selective integrin alpha(5)beta(1) antagonist from Eristocophis macmahoni venom

The disulphide-bond pattern of the heterodimeric disintegrin EMF-IO, a pote nt and selective integrin alpha(5)beta(1) antagonist from Eristocophis macm ahoni venom, was established by combination of amino-acid analysis, N-termi nal sequencing and collision-induced dissociation by nanoelectrospray ioniz ation quadrupole ion-trap MS of fragments isolated by reversed-phase HPLC a fter degradation of EMF-IO with oxalic acid. Each EMF-IO subunit contains f our intrachain disulphide bonds. Two interchain cystine residues join the E MF-IO polypeptides. The intrachain linkages are conserved in monomeric disi ntegrins. A molecular model of EMF-10 was built using averaged NMR co-ordin ates of flavoridin as a template. The active hairpin loops of the EMF-10 su bunits occupy opposite locations at the ends of an elongated disulphide-bon d ladder. In the EMF-10 model the N-terminal polypeptide of EMF-10B is clos e to the RGD-loop of the EMF-10A subunit, suggesting that the N-terminal re gion of the B-subunit could potentially influence the biological activity o f the A-subunit.