Gaegurin 4, a peptide antibiotic of frog skin, forms voltage-dependent channels in planar lipid bilayers.
Gaegurin 4 (GGN4) is a cationic peptide of 37 amino acids (MW 3748) isolated from the skin of Rana rugosa. It has shown a broad spectrum antimicrobial activity in vitro against Gram-negative and -positive bacteria, fungi and protozoa. To understand its mechanism of antimicrobial action, we examined the effect of GGN4 on the membrane conductance and the electrical properties of GGN4-induced pores in planar lipid bilayers under voltage clamp. Natural and synthetic GGN4 (0.01-1 microg/mL) increased the membrane conductance in a concentration-dependent manner, but GGN4 (1-23), an N-terminal fragment of the peptide with little antimicrobial activity, failed to increase the conductance. At symmetrical 100 mM KCI, unitary conductances of about 120 pS were frequently observed. Their current-voltage relations were linear and open state probabilities were close to 1, but longer closing events were seen more frequently at negative voltages. In addition, GGN4-induced pores were selective for cation over anion, the permeability ratio of K+ to Cl- being 6: 1 in neutral and 7: 1 in acidic lipid bilayers. In conclusion, our results indicate that GGN4 forms voltage-dependent and cation-selective pores in planar lipid bilayers. The ionophoric property of GGN4 is likely to contribute to its antimicrobial activity.
Kim
H J
HJ
Department of Pharmacology, College of Veterinary Medicine Seoul National University, Korea.
Han
S K
SK
Park
J B
JB
Baek
H J
HJ
Lee
B J
BJ
Ryu
P D
PD
D000595:Amino Acid Sequence; D000818:Animals; D000900:Anti-Bacterial Agents / Q000378:metabolism / Q000494:pharmacology; D004553:Electric Conductivity; D004594:Electrophysiology; D007473:Ion Channels / Q000378:metabolism*; D008051:Lipid Bilayers / Q000378:metabolism; D008969:Molecular Sequence Data; D010455:Peptides / Q000378:metabolism / Q000494:pharmacology; D011498:Protein Precursors / Q000378:metabolism* / Q000494:pharmacology; D011898:Ranidae / Q000378:metabolism*; D012867:Skin / Q000737:chemistry*
D000900:Anti-Bacterial Agents; D007473:Ion Channels; D008051:Lipid Bilayers; D010455:Peptides; D011498:Protein Precursors; C096396:gaegurin 4