Disulphide-bond pattern and molecular modelling of the dimeric disintegrin EMF-10, a potent and selective integrin α5β1 antagonist from Eristocophis macmahoni venom

The disulphide-bond pattern of the heterodimeric disintegrin EMF-IO, a potent and selective integrin alpha(5)beta(1) antagonist from Eristocophis macmahoni venom, was established by combination of amino-acid analysis, N-terminal sequencing and collision-induced dissociation by nanoelectrospray ionization quadrupole ion-trap MS of fragments isolated by reversed-phase HPLC after degradation of EMF-IO with oxalic acid. Each EMF-IO subunit contains four intrachain disulphide bonds. Two interchain cystine residues join the EMF-IO polypeptides. The intrachain linkages are conserved in monomeric disintegrins. A molecular model of EMF-10 was built using averaged NMR co-ordinates of flavoridin as a template. The active hairpin loops of the EMF-10 subunits occupy opposite locations at the ends of an elongated disulphide-bond ladder. In the EMF-10 model the N-terminal polypeptide of EMF-10B is close to the RGD-loop of the EMF-10A subunit, suggesting that the N-terminal region of the B-subunit could potentially influence the biological activity of the A-subunit.