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Atomic Force Microscopy Imaging and Force Spectroscopy of Supported Lipid Bilayers
Published on: July 22, 2015
Interaction of beta-lactoglobulin with phospholipid bilayers: a molecular level elucidation as revealed by infrared
1Centre de recherches en Sciences et Technologie du Lait (STELA), Faculté des sciences de l'agriculture et de l'alimentation, Université Laval, Pavillon Paul Comtois, Quebec, G1K 7P4, Sainte-Foy, Canada.
Insights
Beta-lactoglobulin (BLG) interacts with milk fat globule membrane (MFGM) lipids, specifically sphingomyelin (SM) and charged phospholipids (PS). BLG causes disorder in SM bilayers and rigidifies PS bilayers, indicating specific protein-lipid interactions.
Area of Science:
- Biochemistry
- Spectroscopy
- Materials Science
Background:
- Milk fat globule membrane (MFGM) is a complex biological structure.
- Beta-lactoglobulin (BLG) is a major milk protein.
- Understanding protein-lipid interactions is crucial for food science and biomaterials.
Purpose of the Study:
- To investigate molecular interactions between BLG and MFGM lipids using FTIR spectroscopy.
- To determine how BLG affects the structure and conformation of different phospholipids.
- To elucidate the mechanisms of BLG-lipid binding.
Main Methods:
- Fourier transform infrared (FTIR) spectroscopy was employed.
- Secondary structure of BLG was monitored via the amide I' band.
- Phospholipid conformation was analyzed through acyl chain and carbonyl bands.
Main Results:
- BLG did not affect neutral phosphatidylcholine (PC) bilayers (DMPC, DPPC) or its own structure.
- BLG interacted with sphingomyelin (SM) bilayers, increasing acyl chain disorder.
- BLG electrostatically interacted with charged phosphatidylserine (PS) bilayers, causing rigidification and dehydration.
Conclusions:
- BLG shows specific interactions with MFGM lipids, influenced by lipid type and charge.
- Hydrophobic interactions drive BLG binding to SM, while electrostatic forces dominate with PS.
- These findings provide molecular insights into protein-lipid interactions in milk.
Abstract:
Fourier transform infrared (FTIR) spectroscopy has been used to study, at a molecular level, the interactions between beta-lactoglobulin (BLG), the most abundant globular protein in milk, and some lipids (sphingomyelin, SM; dimyristoylphosphatidylcholine, DMPC; dipalmytoylphosphatidylcholine, DPPC; dimyristoylphosphatidylserine-sodium salt, DMPS; dipalmitoylphosphatidylserine-sodium salt, DPPS) constituting the milk fat globule membrane (MFGM). The interactions were monitored with respect to alteration in the secondary structure of BLG, as registered by the amide I' band, and phospholipid conformation, as revealed by the acyl chain and carbonyl bands. The results show that neither the conformation nor the thermotropism of neutral bilayers containing DMPC or DPPC is affected by BLG. Reciprocally, the secondary structure and thermal behaviour of pure BLG remain the same in the presence of PC. These results suggest that no interaction occurs between PC and BLG, in agreement with previous studies. However, it is found that BLG interacts with neutral bilayers constituted by milk SM lipids, increasing gauche conformers and thus conformational disorder of the lipid acyl chains. This perturbing effect has been attributed to a partial penetration of BLG into the hydrophobic core of the bilayer, which allows hydrophobic interactions between BLG and SM. Moreover, the fact that SM possesses the same headgroup of PC implies that the head group does not prevent the occurrence of BLG-lipid interactions and other lipid regions can control the binding of BLG to lipids. Furthermore, BLG was found to interact electrostatically with charged bilayers containing PS, leading to a rigidification of the lipid hydrocarbon chains and a dehydration of the interfacial region. This last effect suggests that the protein limits the accessibility of water molecules to the interfacial region of the phospholipids by its presence at the membrane surface.
