Lipid/protein interface

The introduced cysteine residues are found in one of three possible environments (1) on the water-accessible surface, (2) within the protein interior, or (3) at the protein-lipid interface (Karbn and Akabas, 1998). 

Sass, H. J., Btlldt, G., Beckmann, E., Zemlin, F., Van Heel, M., Zeitler, E., Rosenbusch, J. P., Dorset, D. L., and Massalski, A. (1989). Densely packed beta-structure at the protein-lipid interface of porin is revealed by high-resolution cryo-electron microscopy. J. Mol. Biol. 209,171-1... 

The reference 28 authors continue to detail experimental observations that place voltage sensor helices in positions within the membrane. Miller and coworkers conducted site-directed mutagenesis for all residues of helices Sl-S3. ° In these experiments, tryptophan (trp) residues were substituted for each amino acid in turn to determine which residues would be trp-tolerant. These experiments confirmed a-helical conformations for SI and S2 and showed that K+ channel function was altered when trp residues were placed in some (labeled non-trp-tolerant), but not all, positions. The same treatment for helix S3 yielded complex results. At S3 s N-terminal end the distribution of trp-tolerant positions were consistent with an a-helical structure, however, this was not the case at S3 s C-terminal end. Other tests indicated that S3 might be helical for its entire length and that the N-terminal end interfaces with both lipid and protein while the C-terminal end interfaces with water. Comparisons of trp-tolerant or trp-intolerant residues over several different Kv channel... 

In this section, we review our first examinations of tryptophan probing sensitivity and water dynamics in a series of important model systems from simple to complex, which range from a tripeptide [70], to a prototype membrane protein melittin [70], to a common drug transporter human serum albumin [71], and to lipid interface of a nanochannel [86]. At the end, we also give a special case that using indole moiety of tryptophan probes supramolecule crown ether solvation, and we observed solvent-induced supramolecule folding [87]. The obtained solvation dynamics in these systems are linked to properties or functions of these biological-relevant macromolecules. 

Membrane lipids are amphiphatic molecules they contain both a hydrophilic and a hydrophobic moiety. Molecules of this kind can lead to various types of interface. A natural example is the cellular membrane, a bilayer arrangement of such molecules, that marks the frontier between cells. The principal constituents of this membrane are lipids and proteins (Fig. 17.1). 

Molecular structure must be implicated as odorants bind specifically with the sensory receptors called odorant receptors (ORs). The olfactory mucus has proteins called odorant binding proteins (OBPs) that dissolve the odorant molecule in the aqueous/lipid interface of the mucus. The OBPs act as binder molecules to assist the transfer of odorant to the receptor and increase its relative concentration in the mucus relative to inhaled air. They also function to remove used odorants for breakdown and free up the receptor to detect other molecules. 

The alveolar surface represents a thin liquid film formed at the interface between the alveolar gas phase and a liquid hypophase covering the epithelium. This film is stabilised by the alveolar surfactant (AS), consisting mainly of phospholipids and proteins. AS plays an important role in alveolar stabilisation in the process of breathing. It is known that AS components exist as individual molecules and as various lipid and protein/lipid micellar structures present in the so-called hypophase and, according to some researchers, form a continuous lipid monolayer at the water/air interface [e.g. 1-4]. 

Hygroscopic Substance. Perhaps the most distinctive and vitally important surface property of SC is its capacity to absorb up to six times its own weight in water (16, 89, 90). Attempts have been made to associate this property with protein surfaces (20, 91), protein-lipid interfaces (38, 63, 66), or with lipids alone (66, 92). Recently, investigators have emphasized the joint importance of lipids and proteins, or proteoglycan complexes, in hygroscopic properties (16, 66, 92). 

Figure 1. Schematic representation differentiating primary and secondary interactions. Secondary interactions are the result of interactions between regions surrounding the mouth of the active site and regions of the carrier environment surrounding the ligand. A highly charged protein or lipid interface represents an example of substrate exerting secondary effects.

Nino, Ma.R.R., Patino, J.M.R., Sanchez, C., Cejudo, M., and Navarro, J.M. Physicochemical characteristics of food lipids and proteins at fluid-fluid interfaces, Chem. Eng. Commun., 190,15, 2003. 

Preparation of food foams and emulsions requires the creation and stabilization of air-water or oil-water interfaces. Interfaces foimd in food systems contain a range of surface-active molecules and the interactions between these components determine the long-term stability of the foam or emulsion. The most common species present at the interface will be proteins and various small, highly mobile molecules such as surfactants or lipids. Both proteins and surfactants (or lipids) are capable, on their own, of stabilizing interfaces, but they do so by different molecular mechanisms (Wilde et al., 2004). 

Furthermore, Brown (1994) listed the following properties as those that are important in determining the activation of rhodopsin average bilayer thickness see Dratz Subheading 6.2.) lateral compressibility see Litman and Mitchell, below) curvature stresses of the lipid-water and protein-lipid interfaces and electrostatic forces (determined by the charge of the headgroups). 

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... 

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