Snaclec family (C-type lectin-like protein)

General Activity
Common C-type lectins are non-enzymatic proteins that bind carbohydrate in a calcium-dependent manner. They are found extensively throughout plant and animal species, including venom secretions. In snake venom, lectins are classified into true C-type lectins (CTLs) and snaclecs (also known as C-type lectin-like proteins or CLPs) that lack the carbohydrate-binding loop present in true C-type lectins and consequently do not bind sugars (Drickamer, 1999). Based on their biological activity, they can be divided into four subgroups:
1. anticoagulant proteins that specifically bind to coagulation factors IX (F9), X (F10) or thrombin/prothrombin (F2).
2. coagulant metalloproteinase-lectin complex that binds to prothrombin (F2) or coagulation factor X (F10).
3. platelet aggregation agonists, which affect platelet aggregation by binding to GPIb, either alone or in complex with von Willebrand factor (vWF), integrin alpha-2/beta-1 (ITGA2/ITGB1), platelet glycoprotein VI (GP6) and lectin CLEC-2 (CLEC1B).
4. platelet aggregation antagonists, which affect platelet aggregation by binding to GPIb in complex with vWF, and integrin alpha-2/beta-1 (ITGA2/ITGB1).

Snaclecs are mostly heterodimers of alpha (14-15 kDa) and beta (13-14 kDa) subunits, nearly always linked covalently via a disulfide bond. Some heterotetramers have also been described (here. The heterodimers are often further multimerized either non-covalently, or covalently via additional disulfide bonds, to form larger structures. Under physiological conditions many snaclecs can form non-covalent higher order multimers that are much more effective in clustering receptors and activating platelets than the simple covalent multimers might suggest.

The term snaclec has been given to C-type lectin-like proteins (CLPs) and means SNAke C-type LECtinS. It was given by Clemetson et al., 2009 to avoid confusion with classic C-type lectins and to convey information about the hetero- or oligomeric structure.