alpha-Lactalbumin binding and membrane integrity--effect of charge and degree of unsaturation of glycerophospholipids.
Several studies have shown that the physical state of the phospholipid membrane has an important role in protein-membrane interactions, involving both electrostatic and hydrophobic forces. We have investigated the influence of the interaction of the calcium-depleted, (apo)-conformation of bovine alpha-lactalbumin (BLA) on the integrity of anionic glycerophospholipid vesicles by leakage experiments using fluorescence spectroscopy. The stability of the membranes was also studied by measuring surface tension/molecular area relationships with phospholipid monolayers. We show that the degree of unsaturation of the acyl chains and the proportion of charged phospholipid species in the membranes made of neutral and acidic glycerophospholipids are determinants for the association of BLA with liposomes and for the impermeability of the bilayer. Particularly, tighter packing counteracted interaction with BLA, while unsaturation-leading to looser packing-promoted interaction and leakage of contents. Equimolar mixtures of neutral and acidic glycerophospholipids were more permeable upon protein binding than pure acidic lipids. The effect of lipid structure on BLA-membrane interaction and bilayer integrity may throw new light on the membrane disrupting mechanism of a conformer of human alpha-lactalbumin (HAMLET) that induces death of tumour cells but not of normal cells.
Rødland
Ingunn
I
Department of Biomedicine, Section for Biochemistry and Molecular Biology, University of Bergen, Norway.
Halskau
Øyvind
Ø
Martínez
Aurora
A
Holmsen
Holm
H
D000818:Animals; D000838:Anions / Q000737:chemistry / Q000378:metabolism; D002417:Cattle; D020404:Glycerophospholipids / Q000737:chemistry / Q000378:metabolism*; D007768:Lactalbumin / Q000737:chemistry / Q000378:metabolism*; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism; D008081:Liposomes / Q000737:chemistry / Q000378:metabolism; D008567:Membranes, Artificial; D013050:Spectrometry, Fluorescence
D000838:Anions; D020404:Glycerophospholipids; D008051:Lipid Bilayers; D008081:Liposomes; D008567:Membranes, Artificial; D007768:Lactalbumin