title: Effect of repetitive lysine-tryptophan motifs on the  eukaryotic membrane.
abstract: In a previous study, we synthesized a series of peptides containing simple sequence repeats, (KW)(n)-NH(2) (n = 2,3,4 and 5) and determined their antimicrobial and hemolytic activities, as well as their mechanism of antimicrobial action. However, (KW)(5) showed undesirable cytotoxicity against RBC cells. In order to identify the mechanisms behind the hemolytic and cytotoxic activities of (KW)(5), we measured the ability of these peptides to induce aggregation of liposomes. In addition, their binding and permeation activities were assessed by Trp fluorescence, calcein leakage and circular dichrorism using artificial phospholipids that mimic eukaryotic liposomes, including phosphatidylcholine (PC), PC/sphingomyelin (SM) (2:1, w/w) and PC/cholesterol (CH) (2:1, w/w). Experiments confirmed that only (KW)(5) induced aggregation of all liposomes; it formed much larger aggregates with PC:CH (2:1, w/w) than with PC or PC:SM (2:1, w/w). Longer peptide (KW)(5), but not (KW)(3) or (KW)(4), strongly bound and partially inserted into PC:CH compared to PC or PC:SM (2:1, w/w). Calcein release experiments showed that (KW)(5) induced calcein leakage from the eukaryotic membrane. Greater calcein leakage was induced by (KW)(5) from PC:CH than from PC:SM (2:1, w/w) or PC, whereas (KW)(4) did not induce calcein leakage from any of the liposomes. Circular dichroism measurements indicated that (KW)(5) showed higher conformational transition compared to (KW)(4) due to peptide-liposome interactions. Taken together, our results suggest that (KW)(5) reasonably mediates the aggregation and permeabilization of eukaryotic membranes, which could in turn explain why (KW)(5) displays efficient hemolytic activity.
authors: Research Center for Proteineous Materials, Chosun University, Gwangju 501-759, Korea. y_k_park@chosun.ac.kr.
authors: Ramamourthy
authors: R
authors: Gopal
authors: Jong Kook
authors: JK
authors: Lee
authors: Jun Ho
authors: JH
authors: Lee
authors: Young Gwon
authors: YG
authors: Kim
authors: Gwang Chae
authors: GC
authors: Oh
authors: Chang Ho
authors: CH
authors: Seo
authors: Yoonkyung
authors: Y
authors: Park
mesh_terms: D020816:Amino Acid Motifs; D002462:Cell Membrane / Q000737:chemistry*; D002463:Cell Membrane Permeability; D005057:Eukaryotic Cells / Q000737:chemistry*; D008239:Lysine / Q000737:chemistry; D008567:Membranes, Artificial; D008956:Models, Chemical; D010455:Peptides / Q000737:chemistry*; D014364:Tryptophan / Q000737:chemistry
chemical_list: D008567:Membranes, Artificial; D010455:Peptides; D014364:Tryptophan; D008239:Lysine