Conformational study of poly(L-lysine) interacting with acidic phospholipid vesicles.
Circular dichroism measurements were carried out on poly(L-lysine) in the presence of vesicles of the negatively charged phospholipids, phosphatidylserine (PS; from bovine brain), phosphatidic acid (PA; prepared from egg yolk lecithin) and dimyristoylphosphatidylglycerol (DMPG). PS vesicles induced a conformational change in poly(L-lysine) from random coil to alpha-helix structure in 5 mM Tes (pH 7.0), whereas PA vesicles gave rise to beta-structure in the same buffer. The fraction of alpha-helix, F alpha (or beta-structure, F beta), increased with increasing PS (or PA) concentration, reaching a saturation value of about 0.7 (or about 1). Mixed vesicles comprising PS and dilauroylphosphatidylcholine (DLPC) also induced alpha-helix conformation, however, the saturation value of F alpha diminished with decreasing PS content in mixed vesicles. On the other hand, the spectral patterns for poly(L-lysine) in DMPG vesicle suspensions exhibited the coexistence of alpha-helix and beta-structure. Both F alpha and F beta increased with DMPG concentration and reached saturation values of about 0.5. Mixed vesicles composed of DMPG and dimyristoylphosphatidylcholine (DMPC) led to a reduction in F beta, while F alpha remained almost constant. The diversity in ordered structure induced by different phospholipid vesicles suggests the participation of lipid head groups in determining the secondary structure of poly(L-lysine) adsorbed on the vesicular surface.
Fukushima
K
K
Department of Chemistry, Faculty of Science, Fukuoka University, Japan.
Muraoka
Y
Y
Inoue
T
T
Shimozawa
R
R
D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002942:Circular Dichroism; D010712:Phosphatidic Acids; D010713:Phosphatidylcholines; D010715:Phosphatidylglycerols; D010718:Phosphatidylserines; D011107:Polylysine; D011487:Protein Conformation
D010712:Phosphatidic Acids; D010713:Phosphatidylcholines; D010715:Phosphatidylglycerols; D010718:Phosphatidylserines; C015153:1,2-dilauroylphosphatidylcholine; D011107:Polylysine; C042076:1,2-dilauroylphosphatidic acid; C002773:dimyristoylphosphatidylglycerol