A new Kunitz-type snake toxin family associated with an original mode of interaction with the vasopressin 2 receptor.

Background and purpose. Venomous animals express numerous Kunitz-type peptides. The mambaquaretin-1 (MQ1) recently identified from the Dendroaspis angusticeps venom is the most selective antagonist of the arginine-vasopressin V2 receptor (V2R) and the unique Kunitz-type peptide active on a GPCR. We aimed to exploit other mamba venoms to enlarge the V2R-Kunitz peptide family and get insight into the MQ1 molecular mode of action. Experimental approach. We used a bio-guided screening assay to identify novel MQs and placed them phylogenetically. Several newly identified MQs were produced by solid phase peptide synthesis. They were characterized in vitro by binding and functional tests andin vivo by diuresis measurement in rats. Key results. Eight additional MQs were identified with nanomolar affinities for the V2R, all antagonists. MQs form a new subgroup in the Kunitz family, close to the V2R non-active dendrotoxins and to 2 V2R active cobra toxins. Sequence comparison between active and non-active V2R Kunitz peptides highlighted 5 specific V2R positions. Four of them are involved in V2R activity and belong to the 2 large MQ1 loops. We finally determined that 8 positions, part of these 2 loops, interact with the V2R. The variant MQ1-K39A showed specificity for the human versus the rat V2R . Conclusions and implications. A third function and mode of action is now associated with the Kunitz-peptides. The number of MQ1 residues involved in V2R binding is large and may explain its absolute selectivity. MQ1-K39A represents the first step in the improvement of the MQ1 design for medicinal perspective.

Structural insight into hormone recognition and transmembrane signaling by the atrial natriuretic peptide receptor

Atrial natriuretic peptide (ANP) is an endogenous and potent hypotensive hormone that elicits natriuretic, diuretic, vasorelaxant, and anti-proliferative effects, which play a central role in the regulation of blood pressure and volume. To investigate the hormone-binding and membrane signaling mechanisms mediated by the ANP receptor, we elucidated the crystal structures of the ANP receptor extracellular hormone-binding domain (ANPR) complexed with full-length ANP, truncated mutants of ANP, and dendroaspis natriuretic peptide (DNP) isolated from the venom of the green Mamba snake, Dendroaspis angusticeps. The bound peptides possessed pseudo two-fold symmetry to which the tight coupling of the peptide to the receptor and guanylyl cyclase activity was attributed. The crystal structures and our results from kinetic experiments provide insight into the ligand recognition and transmembrane signaling mechanism of the ANP receptor. Our findings provide useful information that can be applied to drug discovery for heart failure therapies.

Enzymatic Activity And Brine Shrimp Lethality Of Venom From The Large Brown Spitting Cobra (Naja Ashei) And Its Neutralization By Antivenom

Objective There has been little focus on the enzymatic and lethal activities of Naja ashei venom and their neutralization by antivenom. This study aimed to determine the snake venom phospholipase A2/svPLA2 activity and brine shrimp lethality of N. ashei venom and their neutralization by two antivenoms (I and II). The venom of other snakes in East Africa including the puff adder (Bitis arietans), green mamba (Dendroaspis angusticeps), black mamba (Dendroaspis polylepis), Egyptian cobra (Naja haje), red spitting cobra (Naja pallida), and the Eastern forest cobra (Naja subfulva) were used for comparison. Results: N. subfulva venom had the highest svPLA2 activity while D. angusticeps venom had the least activity. N. subfulva venom was the most toxic in the 24-hour brine shrimp lethality assay (BSLA), while N. ashei venom was the most toxic in the 48 and 72-hour assays. N. haje venom was the least toxic in all assays. One ml of antivenom I neutralized 0.075 µg of svPLA2 in N. ashei venom compared to 0.051 µg by antivenom II. Antivenom I was ineffective in neutralizing N .ashei venom-induced lethality but 1 ml of antivenom II neutralized 0.21 mg of N. ashei venom.