Omega-conotoxins act at presynaptic membranes, they bind and block voltage-gated calcium channels (Cav). This toxin preferentially blocks P/Q-type calcium channels (Cav2.1/CACNA1A) (IC(50)=0.60 nM) (PubMed:1352986, PubMed:10938268). Shows also an inhibition on Cav2.2/CACNA1A channels (IC(50)=7.0 nM) (PubMed:10938268). Expressed by the venom duct. The presence of a 'disulfide through disulfide knot' structurally defines this protein as a knottin. The cysteine framework is VI/VII (C-C-CC-C-C). Not hydroxylated; hydroxylation, on a synthetic hydroxylated MVIIC, has a significant impact on the oxidative folding but not on the biological activity. Could be used as a diagnostic tool for the autoimmune disease Lambert-Eaton myasthenic syndrome. Belongs to the conotoxin O1 superfamily.