Peptide name : APETx4

Source/Organism : Anthopleura elegantissima

Linear/Cyclic : Linear

Chirality : L

Peptide length: 42

C-terminal modification: Linear

N-terminal modification : Free

Non-natural peptide information:

Assay type : CellTox Green Dye assay

Assay time : 20-h

Activity : Green object count < 100 /mm2 at 20 μM

Cell line : MDA-MB-435S

Cancer type : Skin Cancer

Other activity : Anticancer

Amino acid composition bar chart :

Molecular mass : 4660.3299 Dalton

Aliphatic index : 0.440

Instability index : 14.1619

Hydrophobicity (GRAVY) : 0.0333

Isoelectric point : 8.293

Charge (pH 7) : 1.697

Aromaticity : 21.42

Molar extinction coefficient (cysteine, cystine): (6, 3)

Hydrophobic/hydrophilic ratio : 1.3333

hydrophobic moment : 0.4271

Missing amino acid : A,E,H,M,Q

Most occurring amino acid : G

Most occurring amino acid frequency : 7

Least occurring amino acid : W

Least occurring amino acid frequency : 1

Secondary structure fraction (Helix, Turn, Sheet): (7.1, 33., 45.)

SMILES Notation: CC[C@H](C)[C@H](NC(=O)CNC(=O)[C@@H](NC(=O)[C@@H](NC(=O)[C@H](CCCCN)NC(=O)CNC(=O)[C@H](CS)NC(=O)[C@H](Cc1ccc(O)cc1)NC(=O)[C@H](CS)NC(=O)[C@@H](NC(=O)[C@@H](NC(=O)CN)[C@@H](C)O)[C@@H](C)O)[C@@H](C)O)[C@@H](C)CC)C(=O)N[C@@H](Cc1ccc(O)cc1)C(=O)N[C@@H](Cc1c[nH]c2ccccc12)C(=O)N[C@@H](Cc1ccccc1)C(=O)NCC(=O)N[C@@H](CCCCN)C(=O)N[C@@H](Cc1ccc(O)cc1)C(=O)N[C@@H](CO)C(=O)N[C@@H](CS)C(=O)N1CCC[C@H]1C(=O)N[C@H](C(=O)N[C@@H](CC(N)=O)C(=O)N[C@@H](CCCNC(=N)N)C(=O)NCC(=O)N[C@@H](Cc1ccc(O)cc1)C(=O)N[C@H](C(=O)NCC(=O)N[C@@H](CO)C(=O)N[C@@H](CS)C(=O)N1CCC[C@H]1C(=O)N[C@@H](Cc1ccc(O)cc1)C(=O)N[C@@H](Cc1ccccc1)C(=O)N[C@@H](CC(C)C)C(=O)NCC(=O)N[C@H](C(=O)N[C@@H](CS)C(=O)N[C@@H](CS)C(=O)N[C@@H](Cc1ccc(O)cc1)C(=O)N1CCC[C@H]1C(=O)N[C@H](C(=O)N[C@@H](CC(=O)O)C(=O)O)C(C)C)[C@@H](C)CC)[C@@H](C)O)[C@@H](C)O

1 : Moreels L, et al. APETx4, a Novel Sea Anemone Toxin and a Modulator of the Cancer-Relevant Potassium Channel K_V10.1. Mar Drugs. 2017; 15:(unknown pages). doi: 10.3390/md15090287

Paper title : APETx4, a Novel Sea Anemone Toxin and a Modulator of the Cancer-Relevant Potassium Channel K_V10.1.

Doi : https://doi.org/10.3390/md15090287

Abstract : The human ether-à-go-go channel (hEag1 or K_V10.1) is a cancer-relevant voltage-gated potassium channel that is overexpressed in a majority of human tumors. Peptides that are able to selectively inhibit this channel can be lead compounds in the search for new anticancer drugs. Here, we report the activity-guided purification and electrophysiological characterization of a novel K_V10.1 inhibitor from the sea anemone Anthopleura elegantissima. Purified sea anemone fractions were screened for inhibitory activity on K_V10.1 by measuring whole-cell currents as expressed in Xenopus laevis oocytes using the two-microelectrode voltage clamp technique. Fractions that showed activity on Kv10.1 were further purified by RP-HPLC. The amino acid sequence of the peptide was determined by a combination of MALDI- LIFT-TOF/TOF MS/MS and CID-ESI-FT-ICR MS/MS and showed a high similarity with APETx1 and APETx3 and was therefore named APETx4. Subsequently, the peptide was electrophysiologically characterized on K_V10.1. The selectivity of the toxin was investigated on an array of voltage-gated ion channels, including the cardiac human ether-à-go-go-related gene potassium channel (hERG or Kv11.1). The toxin inhibits K_V10.1 with an IC₅₀ value of 1.1 μM. In the presence of a similar toxin concentration, a shift of the activation curve towards more positive potentials was observed. Similar to the effect of the gating modifier toxin APETx1 on hERG, the inhibition of Kv10.1 by the isolated toxin is reduced at more positive voltages and the peptide seems to keep the channel in a closed state. Although the peptide also induces inhibitory effects on other K_V and Na_V channels, it exhibits no significant effect on hERG. Moreover, APETx4 induces a concentration-dependent cytotoxic and proapoptotic effect in various cancerous and noncancerous cell lines. This newly identified K_V10.1 inhibitor can be used as a tool to further characterize the oncogenic channel K_V10.1 or as a scaffold for the design and synthesis of more potent and safer anticancer drugs.