Naja nivea (Cape Cobra) is endemic to southern Africa. Envenoming by N. nivea is neurotoxic, resulting in fatal paralysis. Its venom composition, however, has not been studied in depth, and specific antivenoms against it remain limited in supply. Applying a protein decomplexation approach, this study unveiled the venom proteome of N. nivea from South Africa. The major components in the venom are cytotoxins/cardiotoxins (~75.6% of total venom proteins) and alpha-neurotoxins (~7.4%), which belong to the three-finger toxin family. Intriguingly, phospholipase A2 (PLA2) was undetected—this is a unique venom phenotype increasingly recognized in the African cobras of the Uraeus subgenus. The work further showed that VINS African Polyvalent Antivenom (VAPAV) exhibited cross-reactivity toward the venom and immunorecognized its toxin fractions. In mice, VAPAV was moderately efficacious in cross-neutralizing the venom lethality with a potency of 0.51 mg/mL (amount of venom completely neutralized per milliliter of antivenom). In the challenge-rescue model, VAPAV prevented death in 75% of experimentally envenomed mice, with slow recovery from neurotoxicity up to 24 h. The finding suggests the potential para-specific utility of VAPAV for N. nivea envenoming, although a higher dose or repeated administration of the antivenom may be required to fully reverse the neurotoxic effect of the venom.
Chemokine CXCL4L1, a homologue of CXCL4, is a more potent antiangiogenic ligand. Its structural property is correlated with the downstream receptor binding. The two chemokines execute their functions by binding the receptors of CXCR3A and CXCR3B. The receptors differ by an extra 51residue extension in the CXCR3B N-terminus. To understand the binding specificity, a GB1 protein scaffold was used to carry different CXCR3 extracellular elements, and artificial CXCL4 and CXCL4L1 monomers were engineered for the binding assay. We first characterized the molten globule property of CXCL4L1. The structural property causes the CXCL4L1 tetramer to dissociate into monomers in low concentrations, but native CXCL4 adopts a stable tetramer structure in solution. In the titration experiments, the combination of the CXCR3A N-terminus and receptor extracellular loop 2 provided moderate and comparable binding affinities to CXCL4 and CXCL4L1, while sulfation on the CXCR3A N-terminal tyrosine residues provided binding specificity. However, the CXCR3B N-terminal extension did not show significant enhancement in the binding of CXCL4 or CXCL4L1. This result indicates that the tendency to form a chemokine monomer and the binding affinity together contribute the high antiangiogenic activity of CXCL4L1.
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