Lipid protein interactions

Investigation of Protein-Lipid Interaction Development During Acid-Induced Milk Coagulation Kinetics... 

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 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. 

Taken together, the field is now well placed to design new biosensors, examine protein-protein and protein-lipid interactions, and sensitively determine protein conformation in living tissues at submicron resolution. These interactions are either impossible or extraordinarily difficult to examine in other ways, and the subcel-lular resolution of FRET-FLIM that allows detection of interactions in specific subcellular compartments may provide insight that... 

Fivaz, M. and Meyer, T. Specific localization and timing in neuronal signal transduction mediated by protein-lipid interactions. Neuron 40 319-330, 2003. 

The scope of my contribution referred to diffusion in enzyme-membrane. The problem of protein-lipids interaction would demand a further lecture. With lipid-protein membranes, there are many phenomena, but diffusion still plays an important role. 

Fat absorption of protein additives has been studied less extensively than water absorption and consequently the available data are meager. Although the mechanism of fat absorption has not been explained, fat absorption is attributed mainly to the physical entrapment of oil (7). Factors affecting the protein-lipid interaction include protein conformation, protein-protein interactions, and the spatial arrangement of the lipid phase resulting from the lipid-lipid interaction. Non-covalent bonds, such as hydrophobic, electrostatic, and hydrogen, are the forces involved in protein-lipid interactions no single molecular force can be attributed to protein-lipid interactions ( ). 

For fat absorption, the measurements have been fewer and more consistent than those reported for water absorption. Therefore, one should be able to examine with more security the data of separate studies. The main problem associated with the fat absorption method appears to be that rarely, if ever, is a food system encountered that involves only the protein-lipid interaction. 

Conformational Assignment of the Red Shift. The ubiquitous appearance of strikingly similar red-shifted Cotton effects in the ORD of membrane systems suggests some structural feature common to all. There are three obvious possibilities in terms of molecular association protein-protein interaction, protein-lipid interaction, and lipid-lipid interaction. All three have been suggested in the literature. 

Biological membranes are always pictured as being very selective barriers separating different biochemical reaction compartments. This high performance transport specificity solely depends on the presence of membrane proteins embedded in the lipid matrix. On the other hand, most membrane proteins cease to function in the absence of lipids. In order to introduce biological transport abilities into artificial membrane systems protein-lipid interactions are of vital interest. The question is how the activity of membrane proteins is affected if they are placed into a polymeric environment. 

From J. T. Segrest and L. D. Kohn, Protein-lipid interactions of the membrane penetrating MN-glycoprotein from the human erythrocyte, Protides of the Biological Fluids, 21st colloquium, ed. by J. Peeters, Pergamon Press, New York, 1973. 

Protein-lipid interaction in retinal-rod outer disc membranes in sonicated vesicles is suggested from comparison of the T1 data of these vesicles with those of extracted liposome preparations from the same source (Brown et al., 1976). Chloroplast thylakoids form micellar structures in chloroform and bilayer structures in water. It was shown by 13C relaxation (Johns et al., 1977) that T1 data are sensitive to this change in secondary structure. As in the... 

So far the bottleneck in producing protein chips seems to be the preparation of the individual proteins, but for this heavily researched area solutions are on the horizon. The advantage of the protein chip approach is that a comprehensive set of individual proteins can be directly screened in vitro for a wide variety of activity, including protein-drug interactions, protein-lipid interactions, and enzymatic assays using a wide range of in vitro conditions - and faster and cheaper than with conventional methods. 

As stated, biological membranes are normally arranged as bilayers. It has, however, been observed that some lipid components of biological membranes spontaneously form non-lamellar phases, including the inverted hexagonal form (Figure 1.9) and cubic phases [101]. The tendency to form such non-lamellar phases is influenced by the type of phospholipid as well as by inserted proteins and peptides. An example of this is the formation of non-lamellar inverted phases by the polypeptide antibiotic Nisin in unsaturated phosphatidylethanolamines [102]. Non-lamellar inverted phase formation can affect the stability of membranes, pore formation, and fusion processes. So-called lipid polymorphism and protein-lipid interactions have been discussed in detail by Epand [103]. 

Transmission of extracellular signals to the cell interior is based on receptor-induced recruitment and assembly of proteins into signaling complexes at the inner leaflet of the plasma membrane. Protein-protein and protein-lipid interactions play a crucial role in the process in which molecular proximity in specially formed membrane subdomains provides the special and temporal constraints that are required for proper signaling. The phospholipid bilayer is not merely a passive hydrophobic medium for this assembly process, but is also a site where the lipid and the protein components are enriched by a dynamic process (see Chapter 5). 

Lipids are often a nuisance in extraction of proteins. For example, in preparing leaf protein concentrate a protein-lipid complex is formed frequently affecting the protein extraction efficiency (16). Nutritionally, the complex is disadvantageous because it resists digestion by proteases (17). Shenouda and Pigott (18) found that the formation of protein-bound lipids can cause a low efficiency of extraction of protein from fish. Hydro-phobic bonding probably plays an important role in protein-lipid interactions. Mohammadzadeh-k et al. (19) reported protein interaction with completely apolar compounds such as aliphatic hydrocarbons. 

Interestingly, it appears that it is easier to induce the formation of a helical hairpin with the tight turn on the lumenal side of the ER membrane than one with the opposite orientation (cytoplasmic turn) i.e., whereas a single Pro is enough to convert the 40-residues long poly (Leu) stretch to a helical hairpin with a lumenal turn, three consecutive prolines are needed for a helical hairpin with a cytoplasmic turn to form (Saaf et al., 2000) (Fig. 2B). If one only considers simple protein—lipid interactions there is no obvious thermodynamic reason why this should be so instead, we favor the view that this reflects a constraint on helical hairpin structure imposed by the Sec machinery. 

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