Solubility hydrophobic domain

Botulinum and tetanus neurotoxins, which are extensively soluble in water, are known to form efficient membrane channels at a low pH in artificial membranes (Hoch et al. 1985 Boquet and Duflot, 1982). Membrane channel formation by a water soluble protein is an intriguing phenomenon, because for water solubility, hydrophobic domains are needed on the surface of a protein whereas for membrane channel formation, adequate hydrophobic segments will be required for the interaction with non-polar membrane bilayer. A major question to be answered is how are the polypeptides integrated in the lipid bilayer. Are the hydrophobic segments of these neurotoxins hidden in aqueous medium which get exposed... 

AChE-R (in purple) Naturally rare, stress-induced variant, which lacks a hydrophobic domain and is incapable of binding to ColQ or PRiMA. Therefore, it remains soluble, and its secreted form shows greater mobility than AChE-S. AChE-R can intra-cellularly interact through its C-terminal tail with the Protein Kinase C Receptor RACK1, a scaffold protein which modifies multiple cellular processes. 

Rieske proteins are constituents of the be complexes that are hydro-quinone-oxidizing multisubunit membrane proteins. All be complexes, that is, bci complexes in mitochondria and bacteria, b f complexes in chloroplasts, and corresponding complexes in menaquinone-oxidizing bacteria, contain three subunits cytochrome b (cytochrome 6e in b f complexes), cytochrome Ci (cytochrome f in b(,f complexes), and the Rieske iron sulfur protein. Cytochrome 6 is a membrane protein, whereas the Rieske protein, cytochrome Ci, and cytochrome f consist of water-soluble catalytic domains that are bound to cytochrome b through a membrane anchor. In Rieske proteins, the membrane anchor can be identified as an N-terminal hydrophobic sequence (13). 

After uptake, lipophilic pollutants tend to move into hydrophobic domains within animals or plants (membranes, lipoproteins, depot fat, etc.), unless they are biotransformed into more polar and water soluble with compounds having low Metabolism of lipophilic compounds proceeds in two stages ... 

Tropoelastin is the soluble precursor of elastin and consists of alternating hydrophobic and hydrophilic peptide domains. The most common amino acids in the hydrophobic domains are Gly, Val, Ala, and Pro, which are often present in repeats of tetra-, penta-, and hexapeptides, such as Gly-Gly-Val-Pro, Gly-Val-Gly-Val-Pro, Gly-Val-Pro-Gly-Val, and Gly-Val-Gly-Val-Ala-Pro, respectively [3, 4]. The hydrophilic domains are mainly composed of lysines interspersed by alanines. 

Referring to a chemical species having two distinct domains with opposing solubility properties (e.g., a charged domain and an apolar or hydrophobic domain). Such molecules often readily form micelles when present in dilute aqueous solutions. 

Lowers solubility of protein at or near isoelectric point or pi, where the protein is in net unionized form some protein may become denatured under these conditions Heat-sensitive proteins expose hydrophobic domains, which exhibit decreased solubility. This process must be reversible if original conformation is required for protein activity... 

Researchers have reasoned that if the water-soluble peptide leu-enkephalin could be conjugated with an oxidizable hydrophobic chain, and further shielded with a hydrophobic domain provided by cholesterol via an ester linkage, the modihed leu-enkephalin could become sufficiently hydrophobic to breach the blood-brain barrier. The oxidation of one of the engineered domains in the brain would produce an ionic form that cannot redistribute back into blood, and is essentially locked in. The ester linkages could then be hydrolyzed by esterases in brain tissues to release biologically active leu-enkephalin (Figure 13.12). 

Enhanced electron transfer quenching has also been observed in copolymers containing both ionic and hydrophobic segments [153], probably as a consequence of static quenching from preferential binding of the redox participants in electrostatically favorable regions of the polymeric aggregate. The hydrophobic domains in such polymers act as traps for hydrophobic quenchers, while the hydrophilic interactions enhance dispersion and solubility [154],... 

Aggregates like polyelectrolyte complexes having positive charges and hydrophobic domains show a broader optimum flocculation concentration range and are considered as new reactive nanoparticles [11-14], Thus, polycations with hydrophobic functionalities represent an interesting class of water-soluble associating polyelectrolytes relevant for controlled stabilization/flocculation of dispersions in numerous industrial applications. 

Microsomal NADH-cytochrome 6b reductase and its acceptor substrate cytochrome 6s are amphipathic proteins, that is, they are each composed of a hydrophobic domain and a soluble domain (74, SS9, 340). The hydrophobic domains serve to anchor the proteins by strong nonco-valent interaction with the lipid bilayer of the microsome. The soluble domains, containing the active sites, FAD or heme, project into the surrounding cytosol. The two domains, in each case, are connected by what is presumed (because of their proteolytic lability) to be rather fl ible sections of polypeptide, imparting considerable mobility to the projecting catalytic domains. The proteins have been shown also to have translational mobility. Interaction between the reductase and the cytochrome is controlled by both types of mobility (341-344)-... 

Amino acid analyses of the two forms are shown in Table VII. They differ from one another by 100 residues, or about 11,000 in molecular weight. The amino acid content of the hydrophobic domain has been calculated by difference, and the composition is dominated by apolar amino acids 74). Treatment of the detergent-extracted enzyme with chymo-trypsin results in a soluble form of the protein its amino acid content is very similar to that of the lysosomal form 74). The spectra of the lysosomal-extracted and the detergent-extracted reductase are Identical in the visible and near-ultraviolet, the extinction coefficient at 461 nm being 10.6 mM cm h Differences between these spectra in the 260-280-nm region are accounted for by the additional tryptophan and tyrosine residues the approximate extinction coefficients at the ultra-... 

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