The Om-toxins are short peptides (23-27 amino acids) purified from the venom of the scorpion Opisthacanthus madagascariensis. Their pharmacological targets are thought to be potassium channels. Like Csalpha/beta (cystine-stabilized alpha/beta) toxins, the Om-toxins alter the electrophysiological properties of these channels; however, they do not share any sequence similarity with other scorpion toxins. We herein demonstrate by electrophysiological experiments that Om-toxins decrease the amplitude of the K+ current of the rat channels Kv1.1 and Kv1.2, as well as human Kv1.3. We also determine the solution structure of three of the toxins by use of two-dimensional proton NMR techniques followed by distance geometry and molecular dynamics. The structures of these three peptides display an uncommon fold for ion-channel blockers, Csalpha/alpha (cystine-stabilized alpha-helix-loop-helix), i.e. two alpha-helices connected by a loop and stabilized by two disulphide bridges. We compare the structures obtained and the dipole moments resulting from the electrostatic anisotropy of these peptides with those of the only other toxin known to share the same fold, namely kappa-hefutoxin1.

APETx1 is a 42-amino acid toxin purified from the venom of the sea anemone Anthopleura elegantissima. This cysteine-rich peptide possesses three disulfide bridges (C4-C37, C6-C30, and C20-C38). Its pharmacological target is the Ether-a-gogo potassium channel. We herein determine the solution structure of APETx1 by use of conventional two-dimensional 1H-NMR techniques followed by torsion angle dynamics and refinement protocols. The calculated structure of APETx1 belongs to the disulfide-rich all-beta structural family, in which a three-stranded anti-parallel beta-sheet is the only secondary structure. APETx1 is the first Ether-a-gogo effector discovered to fold in this way. We therefore compare the structure of APETx1 to those of the two other known effectors of the Ether-a-gogo potassium channel, CnErg1 and BeKm-1, and analyze the topological disposition of key functional residues proposed by analysis of the electrostatic anisotropy. The interacting surface is made of a patch of aromatic residues (Y5, Y32, and F33) together with two basic residues (K8 and K18) at the periphery of the surface. We pinpoint the absence of the central lysine present in the functional surface of the two other Ether-a-gogo effectors.

A novel class of molecular chaperones co‐ordinates the assembly and targeting of complex metalloproteins by binding to an amino‐terminal peptide of the cognate substrate. We have previously shown that the NarJ chaperone interacts with the N‐terminus of the NarG subunit coming from the nitrate reductase complex, NarGHI. In the present study, NMR structural analysis revealed that the NarG(1–15) peptide adopts an α‐helical conformation in solution. Moreover, NarJ recognizes and binds the helical NarG(1–15) peptide mostly via hydrophobic interactions as deduced from isothermal titration calorimetry analysis. NMR and differential scanning calorimetry analysis revealed a modification of NarJ conformation during complex formation with the NarG(1–15) peptide. Isothermal titration calorimetry and BIAcore experiments support a model whereby the protonated state of the chaperone controls the time dependence of peptide interaction. Structured digital abstract • http://mint.bio.uniroma2.it/mint/search/interaction.do?interactionAc=MINT-7557484: NarJT (uniprotkb:http://www.ebi.uniprot.org/entry/P0AF26) and NarG (uniprotkb:http://www.ebi.uniprot.org/entry/P09152) bind (http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0407) by isothermal titration calorimetry (http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0065) • http://mint.bio.uniroma2.it/mint/search/interaction.do?interactionAc=MINT-7557456: NarJT (uniprotkb:http://www.ebi.uniprot.org/entry/P0AF26) and NarG (uniprotkb:http://www.ebi.uniprot.org/entry/P09152) bind (http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0407) by nuclear magnetic resonance (http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0077)

Delta-paluIT1 and delta-paluIT2 are toxins purified from the venom of the spider Paracoelotes luctuosus. Similar in sequence to mu-agatoxins from Agelenopsis aperta, their pharmacological target is the voltage-gated insect sodium channel, of which they alter the inactivation properties in a way similar to alpha-scorpion toxins, but they bind on site 4 in a way similar to beta-scorpion toxins. We determined the solution structure of the two toxins by use of two-dimensional nuclear magnetic resonance (NMR) techniques followed by distance geometry and molecular dynamics. The structures of delta-paluIT1 and delta-paluIT2 belong to the inhibitory cystine knot structural family, i.e. a compact disulfide-bonded core from which four loops emerge. Delta-paluIT1 and delta-paluIT2 contain respectively two- and three-stranded anti-parallel beta-sheets as unique secondary structure. We compare the structure and the electrostatic anisotropy of those peptides to other sodium and calcium channel toxins, analyze the topological juxtaposition of key functional residues, and conclude that the recognition of insect voltage-gated sodium channels by these toxins involves the beta-sheet, in addition to loops I and IV. Besides the position of culprit residues on the molecular surface, difference in dipolar moment orientation is another determinant of receptor binding and biological activity differences. We also demonstrate by electrophysiological experiments on the cloned insect voltage-gated sodium channel, para, heterologuously co-expressed with the tipE subunit in Xenopus laevis oocytes, that delta-paluIT1 and delta-paluIT2 procure an increase of Na+ current. delta-PaluIT1-OH seems to have less effect when the same concentrations are used.