Component of a binary toxin active against Culex and some Aedes mosquito larvae (PubMed:1512580, PubMed:8419297). The individual subunits are not toxic. BinAB binds to the gastric caecum and posterior midgut of C.quinquefasciatus larvae; this subunit alone binds the entire larval gut. Binary toxin internalization into host gut cells requires both proteins (PubMed:1512580). Toxic to Aedes atropalpus mosquito larvae; mortality towards both C.quinquefasciatus and A.atropalpus is maximal by 48 hours. A.aegypti is not very susceptible to this toxin (PubMed:8419297). Forms a heterodimer with BinB. The parasporal crystal protein is produced during sporulation and accumulates as a spore inclusion; crystals are separated from the forespores by a branch of the exosporium across the cell. The matrix of the paraspore is dissolved within 15 minutes following Culex quinquefasciatus larvae feeding. Has an N-terminal beta-trefoil domain and a C-terminal pore-forming domain. The trefoil domain has barrel and cap subdomains; the cap has 3 carbohydrate-binding modules while the barrel is involved in host cell receptor binding. At neutral pH the carbohydrate-binding modules are accessible on the toxin surface but the barrel subdomain is not. Processed by proteases in the mosquito gut, probably at both the N- and C-termini. Belongs to the toxin_10 family.