Component of the heterodimer clotting factor G which may play a role in defense mechanisms against fungi (Probable). Initiates a (1->3)-beta-glucan-sensing clotting pathway whereby the alpha subunit binds to glucans containing (1->3)-beta linkages, which are components of the fungal cell wall, and the beta subunit catalyzes the activation of proclotting enzyme (PubMed:7822328). Clotting factor G is a heterodimer composed of two non-covalently associated subunits, alpha and beta. Expressed in hemocytes (at protein level). In presence of (1->3)-beta-glucan, proteolytically cleaved into a 55kDa and a 17kDa forms. Clotting factor G is a component of the Limulus test used to detect bacterial endotoxins in fluids. Belongs to the glycosyl hydrolase 16 family.