The study of lipid-protein interactions: effect of melittin on phase transition of phosphatidylethanolamine and sensitivity of phospholipases to phase state.
The effects of melittin on the bilayer-to-inverted hexagonal (HII) phase transition of egg phosphatidylethanolamine (EPE) and the influence of the phase state of membrane matrix on hydrolysis of EPE by phospholipases have been studied. The phase transitions were measured using the fluorescent probe N-(7-nitro-2,1,3-benzoxadiazol-4-yl)phosphatidylethanolamine (N-NBD-PE) and differential scanning calorimetry. In the presence of melittin at a lipid-to-melittin molar ratio (R1) of 200, 100, and 20, the phase transition of EPE disappeared, indicating that melittin stabilizes the bilayer structure. In the presence of 10 mol% of cholesterol, the phase transition temperature (TH) decreased and TH was observed even in the presence of melittin at R1 of 200 and 100. The fluorescence intensity of the tryptophan residue of melittin is sensitive to the phase transition and the wavelength of emission maxima shift from 352 to 337 nm upon addition of EPE and EPE-cholesterol (10 mol%) at R1 of 200. Kinetic parameters for phospholipase-catalyzed hydrolysis of EPE in bilayer and HII phases showed that HII phase of EPE is a poorer substrate for phospholipases and that cholesterol decreases the susceptibility of EPE to phospholipases.
Nishiya
T
T
Artificial Cells and Organs Research Centre, McGill University, Montreal, PQ, Canada.
Chou
H L
HL
D004795:Enzyme Stability / Q000187:drug effects; D006868:Hydrolysis; D007700:Kinetics; D008051:Lipid Bilayers / Q000037:antagonists & inhibitors; D008555:Melitten / Q000494:pharmacology*; D010714:Phosphatidylethanolamines / Q000737:chemistry* / Q000494:pharmacology; D010740:Phospholipases / Q000737:chemistry* / Q000187:drug effects; D013050:Spectrometry, Fluorescence
D008051:Lipid Bilayers; D010714:Phosphatidylethanolamines; D008555:Melitten; D010740:Phospholipases