Lipid interactions of acylated tryptophan‐methylated lactoferricin peptides by solid‐state NMR |
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Authors: | Denise Greathouse Vitaly Vostrikov Nicole McClellan Juan Chipollini Jack Lay Rohana Liyanage Taylor Ladd |
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Institution: | Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas 72701, USA |
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Abstract: | Lactoferricin (LfB) is a 25‐residue innate immunity peptide released by pepsin from the N‐terminal region of bovine lactoferrin. A smaller amidated peptide, LfB6 (RRWQWR‐NH2) retains antimicrobial activity and is thought to constitute the “antimicrobial active‐site” (Tomita, Acta Paediatr Jpn. 1994; 36 : 585–91). Here we report on N‐acylation of 1‐Me‐Trp5‐LfB6, Cn‐RRWQ1‐Me‐W]R‐NH2, where Cn is an acyl chain having n = 0, 2, 4, 6 or 12 carbons. Tryptophan 5 (Trp5) was methylated to enhance membrane binding and to allow for selective deuteration at that position. Peptide/lipid interactions of Cn‐RRWQ1‐Me‐W ]R‐NH2 (deuterated 1‐Me‐Trp5 underlined), were monitored by solid state 31P NMR and 2H NMR. The samples consisted of macroscopically oriented bilayers of mixed neutral (dimyristoylphosphatidylcholine, DMPC) and anionic (dimyristoylphosphatidylglycerol, DMPG) lipids in a 3:1 ratio with Cn‐RRWQ&1‐Me‐W ]R‐NH2 peptides added at a 1:25 peptide to lipid ratio. 2H‐NMR spectra reveal that the acylated peptides are well aligned in DMPC:DMPG bilayers. The 2H NMR quadrupolar splittings suggest that the 1‐Me‐Trp is located in a motionally restricted environment, indicating partial alignment at the membrane interface. 31P‐NMR spectra reveal that the lipids are predominantly in a bilayer configuration, with little perturbation by the peptides. Methylation alone, in C0‐RRWQ1‐Me‐W ]R‐NH2, resulted in a 3–4 fold increase in antimicrobial activity against E. coli. N‐acylation with a C12 fatty acid enhanced activity almost 90 fold. Copyright © 2008 European Peptide Society and John Wiley & Sons, Ltd. |
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Keywords: | acylated antimicrobial peptide arginine lactoferricin lipid bilayer 1‐methyl‐tryptophan solid‐state NMR tryptophan |
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