Complement-activating protein in cobra venom. It is a structural and functional analog of complement component C3b, the activated form of C3. It binds factor B (CFB), which is subsequently cleaved by factor D (CFD) to form the bimolecular complex OVF/Bb. OVF/Bb is a C3/C5 convertase that cleaves both complement components C3 and C5. Structurally, it resembles the C3b degradation product C3c, which is not able to form a C3/C5 convertase. Unlike C3b/Bb, OVF/Bb is a stable complex and completely resistant to the actions of complement regulatory factors H (CFH) and I (CFI). Therefore, OVF continuously activates complement (By similarity). As a result, OVF exhibits complement-depleting activity. Heterotrimer of alpha, beta and gamma chains; disulfide-linked. May be active with factor B in the presence of factor D. Expressed by the venom gland. First processed by the removal of 4 Arg residues by furin-type protease, forming two chains, alpha and gamma/beta precursor, linked by a disulfide bond. Probably, a cobrin-like protease cleaves the C3a-like domain and then the C3d-like domain, generating the mature venom factor (OVF) (By similarity). The beta chain is not glycosylated. Belongs to the venom complement C3 homolog family.