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.