Protein with lipids, interaction

TiTuch of our understanding of the phase behavior of insoluble - monolayers of lipids at the air-water interface is derived from Adam s studies of fatty acid monolayers (I). It is now clear that the phase behavior of phospholipid monolayers (2) parallels that of the fatty acids we make use of these structure variations in our study of the interactions of phosphatidylcholine (lecithin) monolayers with proteins. Because of the biological significance of the interfacial behavior of lipids and proteins, there is a long history of studies on such systems. When Adam was studying lipid monolayers, other noted contemporary surface chemists were studying protein monolayers (3) and the interactions of proteins with lipid monolayers (4). The latter interaction has been studied by many so-called 4 penetration experiments where the protein is injected into the substrate below insoluble lipid monolayers that are spread on the... 

It seems to be a general rule that, as far as possible, hydrophobic side chains are buried in the interior of protein molecules leaving the polar and charged side chains on the surface. Proteins are, in the main, close packed structures and the hydrophobic amino acids take up space without interacting with water so that they are useful in providing bulk and shape to the interior of the molecule. However, there are usually more non-polar side chains than can be accommodated in the interior and some are exposed on the surface. If these are concentrated in a particular area to give a hydrophobic patch they may be important in the development of quaternary structure and also in the association of proteins with lipids as in membrane structures. 

Fantini J. Interaction of proteins with lipid rafts through glycolipid-binding domains biochemical background and potential therapeutic applications. CurrMed Chem. 2007 14(27) 2911-2917. 

The situation is even worse for membrane lipids. Not a single, naturally occurring phospholipid with unsaturated hydrocarbon chains has yet been crystallized. However, nearly 40 crystal structures of closely related synthetic glycerolipids with saturated hydrocarbon chains have been solved by X-ray. On the structural level, little is known about the interactions of proteins with lipid bilayer environments. Detergent molecules have been detected in some of the X-ray structures, and a small number of studies discuss lipids bound to proteins. An example is cytochrome C oxidase crystals, where the lipids were found to be arranged in a bilayer structure. 

Newton, A.C., Interaction of proteins with lipid headgroups lessons from protein kinase C, Annu. Rev. Biophys. Biomol. Struct., 22, 1, 1993. 

Protems can be physisorbed or covalently attached to mica. Another method is to innnobilise and orient them by specific binding to receptor-fiinctionalized planar lipid bilayers supported on the mica sheets [15]. These surfaces are then brought into contact in an aqueous electrolyte solution, while the pH and the ionic strength are varied. Corresponding variations in the force-versus-distance curve allow conclusions about protein confomiation and interaction to be drawn [99]. The local electrostatic potential of protein-covered surfaces can hence be detemiined with an accuracy of 5 mV. 

Bilayer phase transitions are sensitive to the presence of solutes that interact with lipids, including multivalent cations, lipid-soluble agents, peptides, and proteins. 

TABLE 6 Specific Features of S-Layer Proteins Governing Interactions with Lipid Membranes... 

These assumptions were confirmed by the electrophoresis study of the washed creams. Electrophoresis of purified fat globules is a convenient method to characterize and quantify proteins adsorbed at the oil-water interface [35]. Electrophoretic data indicate that no casein, nor whey proteins, were adsorbed at the surface of raw-milk fat globule. Upon homogenization, caseins adsorbed preferentially at the lipid-water interface. In this case, bound a-lactalbumin accounted for 16% of the total interfacial proteins. Heat treatment also induced the interaction of proteins with the fat globules. The amount of bound proteins (per mg of lipids) for heated raw milk was half that for homogenized milk. 

The method utilizing ID NMR is simple and eonvenient. Henee the NMR method diseussed here ean be applied to the systematie investigation of the membrane irug inter-aetions, elosely related to the vital function in biomembranes. It is expected that the application can be extended to the lipid-peptide interaction and protein uptake. We are now applying the method to apolipoprotein binding with lipid bilayers and emulsions. Preferential protein binding sites in membranes can be specified by NMR on the molecular level. 

New developments in immobilization surfaces have lead to the use of SPR biosensors to monitor protein interactions with lipid surfaces and membrane-associated proteins. Commercially available (BIACORE) hydrophobic and lipophilic sensor surfaces have been designed to create stable membrane surfaces. It has been shown that the hydrophobic sensor surface can be used to form a lipid monolayer (Evans and MacKenzie, 1999). This monolayer surface can be used to monitor protein-lipid interactions. For example, a biosensor was used to examine binding of Src homology 2 domain to phosphoinositides within phospholipid bilayers (Surdo et al., 1999). In addition, a lipophilic sensor surface can be used to capture liposomes and form a lipid bilayer resembling a biological membrane. 

The squaraine probe 9g was tested for its sensitivity to trace the formation of protein-lipid complexes [57]. The binding of dye 9g to model membranes composed of zwitter-ionic lipid phosphatidylcholine (PC) and its mixtures with anionic lipid cardiolipin (CL) in different molar ratios was found to be controlled mainly by hydrophobic interactions. Lysozyme (Lz) and ribonuclease A (RNase) influenced the association of 9g with lipid vesicles. The magnitude of this effect was much higher... 

The dicyanomethylene-squaraine dye 41e was found to be highly sensitive to trace protein-lipid interactions [109]. Lysozyme association with the lipid bilayer leads to a noticeable decrease in the fluorescence intensity of 41e. In a separate... 

Ioffe VM, Gorbenko GP, Tatarets AL, Patsenker LD, Terpechnig EA (2006) Examining protein-lipid interactions in model systems with a new squarylium fluorescent dye. J Fluoresc 16 547-554... 

The 15N spectral peaks of fully hydrated [15N]Gly-bR, obtained via cross-polarization, are suppressed at 293 K due to interference with the proton decoupling frequency, and also because of short values of T2 in the loops.208 The motion of the TM a-helices in bR is strongly affected by the freezing of excess water at low temperatures. It is shown that motions in the 10-j-is correlation regime may be functionally important for the photocycle of bR, and protein-lipid interactions are motionally coupled in this dynamic regime. 

FRET-FLIM has been applied to numerous biological problems, centering on protein-protein interactions, protein conformation, posttranslational modifications, and activation state of enzymes, with lipid microdomains. Each of these applications takes advantage... 

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