8.B.9.1.1
Cycseine-rich venom protein, Triflin.  Blocks contraction of smooth muscle elicited by high potassium-induced depolarization.  May also target voltage-gated calcium channels (Ca_v) in smooth muscle cells.  The crystal structure of triflin, a snake venom derived blocker of high K⁺-induced artery contraction has been solved at 2.4A resolution. Triflin consists of two domains. The first 163 residues form a large globular body with an αβα sandwich core which resembles pathogenesis-related proteins of group-1 (PR-1). Two glutamic acid-associated histidine residues are located in an elongated cleft. A Cd²⁺ resides in this binding site, and forms a five-coordination sphere. The subsequent cysteine-rich domain adopts a rod-like shape, which is stabilized by five disulfide bridges. Hydrophobic residues, which may obstruct the target ion channel, are exposed to the solvent. A concave surface, which is surrounded by these two domains, may play a role in the binding to the target receptor, leading to ion channel blockage. The C-terminal cysteine-rich region has a similar tertiary structure to voltage-gated potassium channel blocker toxins such as BgK and ShK (Shikamoto et al. 2005).