Peptide name : Peptide XT-7

Source/Organism : Western clawed frog

Linear/Cyclic : Linear

Chirality : Mix

Peptide length: 18

C-terminal modification: Linear

N-terminal modification : Amidation

Non-natural peptide information: None

Assay type : Lactate dehydrogenase assay

Assay time : 1h

Activity : LD50 : 20 µM

Cell line : HepG2

Cancer type : Liver cancer

Other activity : Anti-microbial activity

Amino acid composition bar chart :

Molecular mass : 1777.1989 Dalton

Aliphatic index : 1.788

Instability index : -9.4222

Hydrophobicity (GRAVY) : 1.1222

Isoelectric point : 10.002

Charge (pH 7) : 1.7581

Aromaticity : 0

Molar extinction coefficient (cysteine, cystine): (0, 0)

Hydrophobic/hydrophilic ratio : 3.5

hydrophobic moment : -1.516

Missing amino acid : C,R,W,H,Q,T,M,E,F,D,Y

Most occurring amino acid : L

Most occurring amino acid frequency : 6

Least occurring amino acid : P

Least occurring amino acid frequency : 1

Secondary structure fraction (Helix, Turn, Sheet): (0.5, 0.3, 0.4)

SMILES Notation: CC[C@H](C)[C@H](NC(=O)[C@H](CCCCN)NC(=O)[C@H](CC(C)C)NC(=O)[C@H](CC(C)C)NC(=O)[C@@H]1CCCN1C(=O)CNC(=O)[C@H](CC(C)C)NC(=O)[C@H](CC(C)C)NC(=O)CN)C(=O)N[C@@H](C)C(=O)N[C@@H](C)C(=O)N[C@@H](CCCCN)C(=O)N[C@H](C(=O)NCC(=O)N[C@@H](CO)C(=O)N[C@@H](CC(N)=O)C(=O)N[C@@H](CC(C)C)C(=O)N[C@@H](CC(C)C)C(=O)O)C(C)C

1 : Conlon JM, et al. Design of potent, non-toxic antimicrobial agents based upon the naturally occurring frog skin peptides, ascaphin-8 and peptide XT-7. Chem Biol Drug Des. 2008; 72:58-64. doi: 10.1111/j.1747-0285.2008.00671.x

Paper title : Design of potent, non-toxic antimicrobial agents based upon the naturally occurring frog skin peptides, ascaphin-8 and peptide XT-7.

Doi : https://doi.org/10.1111/j.1747-0285.2008.00671.x

Abstract : The frog skin peptides, ascaphin-8 (GFKDLLKGAAKALVKTVLF.NH(2)) and XT-7 (GLLGPLLKIAAKVGSNLL.NH(2)), show broad-spectrum antimicrobial activity but their therapeutic potential is limited by toxicity against mammalian cells. Circular dichroism spectra demonstrate that the peptides adopt an amphipathic alpha-helical conformation in a membrane-mimetic solvent. This study has investigated the cytolytic properties of analogs containing selected amino acid substitutions that increase cationicity while maintaining amphipathicity. Substitutions at Ala(10), Val(14), and Leu(18) in ascaphin-8 by either L-Lys or D-Lys produced peptides that retained antimicrobial activity against the bacteria Escherichia coli and Staphylococcus aureus and the opportunistic yeast pathogen, Candida albicans but showed appreciably reduced toxicities (>10-fold) against human erythrocytes, HepG2 hepatoma-derived cells, and L929 fibroblasts. The improved therapeutic index of the L-Lys(18) and D-Lys(18) analogs correlated with a decrease in % helicity and in effective hydrophobicity. Substitution of Gly(4) by L-Lys in XT-7 produced an analog with high potency against micro-organisms (MIC < or = 25 microM) but low cytolytic activity against erythrocytes (LD(50) > 500 microM) and this increase in therapeutic index also correlated with decreased helicity and hydrophobicity. Analogs of XT-7 with increased cationicity, containing multiple substitutions by L-Lys, not only displayed increased antimicrobial potencies, particularly against Candida albicans (MIC < or = 6 microM), but also increased hemolytic activities.