Tài liệu Báo cáo Y học: The effects of ring-size analogs of the antimicrobial peptide gramicidin S

The effects of ring-size analogs of the antimicrobial peptide

gramicidin S on phospholipid bilayer model membranes

and on the growth of Acholeplasma laidlawii B

Monika Kiricsi1

, Elmar J. Prenner1,2, Masood Jelokhani-Niaraki1,2,*, Ruthven N. A. H. Lewis1

,

Robert S. Hodges1,2,† and Ronald N. McElhaney1,2

1

Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada; 2

Protein Engineering Network of Centers of

Excellence, University of Alberta, Edmonton, Alberta, Canada

We have examined the effects of three ring-size analogs of the

cyclic b-sheet antimicrobial peptide gramicidin S (GS) on the

thermotropic phase behavior and permeability of phos￾pholipid model membranes and on the growth of the cell

wall-less Gram-positive bacteria Acholeplasma laidlawii B.

These three analogs have ring sizes of 10 (GS10), 12 (GS12)

or 14 (GS14) amino acids, respectively. Our high-sensitivity

differential scanning calorimetric studies indicate that all

three of these GS analogs perturb the gel/liquid-crystalline

phase transition of zwitterionic phosphatidylcholine

(PtdCho) vesicles to a greater extent than of zwitterionic

phosphatidylethanolamine (PtdEtn) or of anionic phos￾phatidylglycerol (PtdGro) vesicles, in contrast to GS itself,

which interacts more strongly with PtdGro than with Ptd￾Cho and PtdEtn bilayers. However, the relative potency of

the perturbation of phospholipid phase behavior varies

markedly between the three peptides, generally decreasing in

the order GS14 > GS10 > GS12. Similarly, these three

GS ring-size analogs also differ considerably in their ability

to cause fluorescence dye leakage from phospholipid vesi￾cles, with the potency of permeabilization also generally

decreasing in the order GS14 > GS10 > GS12. Finally,

these GS ring-size analogs also differentially inhibit the

growth of A. laidlawii with growth inhibition also decreasing

in the order GS14 > GS10 > GS12. These results indicate

that the relative potencies of GS and its ring-size analogs in

perturbing the organization and increasing the permeability

of phospholipid bilayer model membranes, and of inhibiting

the growth of A. laidlawii Bcells, are at least qualitatively

correlated, and provide further support for the hypothesis

that the primary target of these antimicrobial peptides is the

lipid bilayer of the bacterial membrane. The very high anti￾microbial activity of GS14 against the cell wall-less bacteria

A. laidlawii as compared to various conventional bacteria

confirms our earlier suggestion that the avid binding of this

peptide to the bacterial cell wall is primarily responsible for

its reduced antimicrobial activity against such organisms.

The relative magnitude of the effects of GS itself, and of the

three ring-size GS analogs, on phospholipid bilayer organi￾zation and cell growth correlate relatively well with the

effective hydrophobicities and amphiphilicities of these

peptides but less well with their relative charge density,

intrinsic hydrophobicities or conformational flexibilities.

Nevertheless, all of these parameters, as well as others, may

influence the antimicrobial potency and hemolytic activity of

GS analogs.

Keywords: antimicrobial peptides; gramicidin S; phospholi￾pid bilayers; membranes.

Gramicidin S (GS) is a cyclic decapeptide of primary

structure [cyclo-(Val-Orn-Leu-D-Phe-Pro)2] first isolated

from Bacillus brevis [1] and is one of a series of

antimicrobial peptides produced by this microorganism

[2,3]. GS exhibits potent antibiotic activity against a broad

spectrum of both Gram-negative and Gram-positive

bacteria, as well as against several pathogenic fungi [4–

7]. Unfortunately, GS is rather nonspecific in its actions

Correspondence to R. N. McElhaney, Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7.

Fax: +1 780 4920095, E-mail: [email protected]

Abbreviations: GS, gramicidin S; Myr2Gro-PCho, dimyristoylglycerophosphocholine; Myr2Gro-PEtn, dimyristoylglycerophosphoethanolamine;

Myr2Gro-PGro, dimyristoylglycerophosphoglycerol; DSC, differential scanning calorimetry; La, lamellar liquid-crystalline phase; Lb or Lb¢

,

lamellar gel phase with untilted or tilted hydrocarbon chains, respectively; LC or LC¢

, lamellar crystalline phase with untilted or tilted hydrocarbon

chains, respectively; Pb¢

, lamellar rippled gel phase with tilted hydrocarbon chains; PtdCho, phosphatidylcholine; PtdEtn, phosphatidylethanol￾amine; PtdGro, phosphatidylglycerol; PamOleGro-PCho, 1-palmitoyl-2-oleoyl-glycerophosphocholine; PamOleGro-PEtn, 1-palmitoyl￾2-oleoyl-glycerophospholamine; PamOleGro-PGro, 1-palmitoyl-2-oleoyl-glycerophosphoglycerol.

*Present address: Department of Chemistry, Wilfred Laurier University, Waterloo, Ontario, Canada N2L 3C5.

Present address: Department of Biochemistry and Molecular Genetics, University of Colorado, Health Sciences Center, 4200 East Ninth Avenue,

Denver, CO 80262, USA.

(Received 9 August 2002, revised 9 October 2002, accepted 15 October 2002)

Eur. J. Biochem. 269, 5911–5920 (2002) FEBS 2002 doi:10.1046/j.1432-1033.2002.03315.x