The 26-residue peptide of sequence KEALYILMVLGFFGFFTLGILSYIR, which contains the single putative transmembrane domain of a small protein that is associated with slow voltage-gated K+ channels, has been incorporated in bilayers of dimyristoylphosphatidylcholine by dialysis from 2-chloroethanol to form complexes of homogeneous lipidpeptide ratio. Fourier transform infrared spectroscopy indicates that the peptide is integrated in the lipid bilayer wholly in a @-sheet conformation. The electron spin resonance spectra of spin-labeled lipids in the lipidpeptide complexes contain a component corresponding to lipids whose chains are motionally restricted in a manner similar to those of lipids at the hydrophobic surface of integral transmembrane proteins. From the dependence of the lipid spin label spectra on the lipidpeptide ratio of the complexes, it is found that ca. 2.5 lipids per peptide monomer, independent of the species of spin-labeled lipid, are motionally restricted by direct interaction with the peptide in the bilayer. This value would be consistent with, e.g., a @-barrel structure for the peptide in which the @-strands either are strongly tilted or have a reverse turn at their center. A preferential selectivity of interaction with the peptide is observed for the negatively charged spin-labeled lipids phosphatidic acid, stearic acid, and phosphatidylserine, which indicates close proximity of the positively charged residues at the peptide termini to the lipid headgroups. The saturation-transfer electron spin resonance spectra of the peptide spin-labeled at a cysteine residue replacing Leu18 evidence rather slow rotational diffusion in the lipid complexes. This indicates that the presumably enclosed @-sheet units of the peptide are aggregated in oligomeric assemblies in the lipid bilayer. The results suggest a way in which one type of channel unit may be integrated in the membrane.Ion channels are generally large, often multimeric, proteins containing many transmembrane segments (Stephenson, 1991). In spite of the molecular complexity, it is likely that the channel itself is lined with a limited range of, possibly homologous, transmembrane segments. Correlating with thls, it is found that certain relatively short synthetic peptides, of sequences resembling those of putative pore-lining segments, are able to sustain channel activity when incorporated in lipid bilayers (Montal, 1990;Ben-Efraim et al., 1993). Such synthetic peptides are therefore suitable models for studying particular aspects of channel structure and assembly by using biophysical or biochemical techniques. The direct relevance to native channels depends, of course, on the correct identification of the pore-lining transmembrane segments.In addition to the complex channel proteins mentioned above, the DNA clone encoding a small protein associated with a slowly activating voltage-gated potassium channel has been identified in rat kidney (Takumi et al., 1988). This protein, Z s~, contains only 130 amino acids with a single putative 23-residu...

Lipid-peptide interactions with the 27-residue peptide of sequence KLEALYILMVLGFFGFFTLGIMLSYIR reconstituted as beta-sheet assemblies in dimyristoylphosphatidylcholine bilayers have been studied by electron spin resonance (ESR) spectroscopy with spin-labeled lipids. The peptide corresponds to residues 42-68 of the IsK voltage-gated K+ channel protein and contains the single putative transmembrane span of this protein. Lipid-peptide interactions give rise to a second component in the ESR spectra of lipids spin-labeled on the 14C atom of the chain that corresponds to restriction of the lipid mobility by direct interaction with the peptide assemblies. From the dependence on the lipid/peptide ratio, the stoichiometry of lipid interaction is found to be about two phospholipids/peptide monomer. The sequence of selectivity for lipid association with the peptide assemblies is in the order phosphatidic acid > stearic acid = phosphatidylserine > phosphatidylglycerol = phosphatidylcholine. Comparison with previous data for a corresponding 26-residue mutant peptide with a single deletion of the apolar residue Leu2 (Horvath et al., 1995. Biochemistry 34:3893-3898), indicates a very similar mode of membrane incorporation for native and mutant peptides, but a strongly modified pattern and degree of specificity for the interaction with negatively charged lipids. The latter is interpreted in terms of the relative orientations of the charged amino acid side chains in the beta-sheet assemblies of the native and deletion-mutant peptides.

In (Andonov et al., 2012) a Generalized Net (see (Atanassov, 2003, 2007)) model of processes, related to tracking the changes in health status of adult patients has been presented. The contemporary state-of-the-art of the telecommunications and navigation technologies allow this model to be extended to the case of active and mobile patient. This enforces the inclusion of patient's current location as a new and significant variable of the model. Various opportunities are considered for the retrieval of this information, with a focus on the optimal ones, and a refined Generalized Net model is proposedt. .