Novel svVEGF isoforms from Macrovipera lebetina venom interact with neuropilins.

Increased vascular permeability and vasodilation are responses usually elicited by snake envenomation. In this report, we isolated from Macroviperalebetina venom two protein groups designated IC1 (Increasing Capillary1) and IC2 based on their activities on capillary permeability. Mass spectrometry analysis showed that IC1 contained four major proteins of 23,650, 24,306, 24,589 and 24,718Da, whereas IC2 contained three major proteins of 25,101, 25,194 and 25,298Da. N-terminal amino-acid sequencing revealed that IC1 and IC2 belong to the snake venom VEGF (svVEGF) family. IC1 and IC2 had a marked specificity for VEGFR-2, with affinities in the nanomolar range. Interestingly, they also bind to NRP1 and NRP2, with affinities in the micromolar range. This is the first report demonstrating that M. lebetina encodes several distinct svVEGFs, endowed with a capacity to interact with neuropilins. IC1 and IC2 could be valuable tools to understand the molecular properties of angiogenic factors and their receptors.

A new type of scorpion Na+-channel-toxin-like polypeptide active on K+ channels.

We have purified and characterized two peptides, named KAaH1 and KAaH2 (AaH polypeptides 1 and 2 active on K+ channels, where AaH stands for Androctonus australis Hector), from the venom of A. australis Hector scorpions. Their sequences contain 58 amino acids including six half-cysteines and differ only at positions 26 (Phe/Ser) and 29 (Lys/Gln). Although KAaH1 and KAaH2 show important sequence similarity with anti-mammal beta toxins specific for voltage-gated Na+ channels, only weak beta-like effects were observed when KAaH1 or KAaH2 (1 microM) were tested on brain Nav1.2 channels. In contrast, KAaH1 blocks Kv1.1 and Kv1.3 channels expressed in Xenopus oocytes with IC50 values of 5 and 50 nM respectively, whereas KAaH2 blocks only 20% of the current on Kv1.1 and is not active on Kv1.3 channels at a 100 nM concentration. KAaH1 is thus the first member of a new subfamily of long-chain toxins mainly active on voltage-gated K+ channels. NMR spectra of KAaH1 and KAaH2 show good dispersion of signals but broad lines and poor quality. Self-diffusion NMR experiments indicate that lines are broadened due to a conformational exchange on the millisecond time scale. NMR and CD indicate that both polypeptides adopt a similar fold with alpha-helical and b-sheet structures. Homology-based molecular models generated for KAaH1 and KAaH2 are in accordance with CD and NMR data. In the model of KAaH1, the functionally important residues Phe26 and Lys29 are close to each other and are located in the alpha-helix. These residues may constitute the so-called functional dyad observed for short alpha-KTx scorpion toxins in the beta-sheet.