Recombinant expression of crotoxin and comparison to native crotoxin as immunogens for anti-crotalid antivenoms

The crotoxin complex is identified as the primary lethal toxin in various species of rattlesnakes. It comprises two subunits: CtxA, a non-toxic protein, and CtxB, a minimally toxic enzymatic phospholipase A₂. These components exert neurotoxic effects by disrupting neuromuscular transmission, specifically by inhibiting the release of acetylcholine, thereby causing flaccid paralysis of the muscles. Due to crotoxin's high lethality, variable presence, and proportion within crotalid venoms, considerable interest has been directed toward its inhibition. In this context, the heterologous expression of a recombinant fusion protein designated as rCtxBA, which incorporates the amino acid sequences of both CtxA and CtxB subunits of crotoxin, has been documented. The rCtxBA protein was recombinantly expressed, recovered, and subsequently purified. New Zealand rabbits were immunized with the recombinants rCtxBA, rCTxB, and the native CtxBA. ELISA and Western blot analyses revealed that the anti-crotoxin antibodies specifically recognized venoms containing crotoxin by binding to both conformational and linear epitopes of crotoxin-like or related phospholipases. In vivo neutralization assays performed in mice demonstrated efficacy of the anti-rCtxBA antibodies against venoms from Crotalus mictlantecuhtli, C. scutulatus salvini, and C. tzabcan-species known to contain crotoxin-with ED₅₀ values of 2.8, 7.8, and 2.5 mg/3LD₅₀, respectively. Conversely, no neutralization effect was observed against the venom of C. molossus nigrescens, a species lacking crotoxin in its venom profile. These findings substantiate that native crotoxin, present in whole crotalid venoms, can be neutralized using recombinant crotalid antigens, thereby facilitating the development of effective neutralizing antibodies.