Amphipathic protein

Many biomolecules are amphipathic proteins, pigments, certain vitamins, and the sterols and phospholipids of membranes all have polar and nonpolar surface regions. Structures composed of these molecules are stabilized by hydrophobic interactions among the non-... 

In the chemosensory sensillum, even lipophilic pheromones and odorants have to reach the receptor membranes across the receptor lymph. The receptor lymph surrounding the receptor membranes is rich in small amphipathic proteins secreted from... 

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)-... 

The mechanism for NADH-cytochrome bs reductase described in Section VII,B was worked out with the soluble enzyme, and the question of its applicability to the interaction of the amphipathic proteins can now be considered. 

Rebinding of the reductase and the cytochrome b to liposomes in a ratio of 1 13 completely restores the activity, inhibited in solution by polymerization. Thus, the phospholipid is an essential component in the interaction of the amphipathic proteins (343). The rate of reduction of cytochrome bs is dependent on its concentration in the microsome and on... 

Generalized structure of a lipoprotein molecule showing the distribution of polar components in an outer shell composed of free cholesterol, phospholipids, and amphipathic proteins and in an inner core composed of neutral triacylglycerols and cholesteryl esters. Phospholipids are oriented with polar head groups toward the aqueous environment and hydrophobic tails toward the neutral core, analogous to their positioning in the outer leaflet of the typical cell membrane. 

These observations are consistent with the mosaic model of the membrane that was derived from monolayer studies (2, 4, 5, 12, 13). Therein, the structural or bimodal (amphipathic) protein in the membrane (natural or artificial) interacts with the polar peripheries of the polymeric lipid structures alongside the protein. The EPR data of Jost et al. (29) support this concept, i.e., an appreciable portion of the lipid is in lateral hydrophilic bonding with the protein whereas the other lipid is free, probably within the lipid cluster, and preserves the lipid character. 

Lipids are only sparingly soluble in water, and the movement of lipids from one organ to another through the bloodstream requires a transport system that uses plasma lipoproteins. Lipoprotein particles consist of a core of hydrophobic lipids surrounded by amphipathic proteins, phospholipids, and cholesterol (Figure 18.8). There are four major classes of human plasma lipoproteins ... 

An alternative approach consists in reconstitution of the membrane protein in bilayer-mimicking environments, i.e., self-assembling lipid bilayer nanodiscs (Fig. lb). Nanodiscs consist of a small portion of membrane bilayer that has been solubilized by the addition of two amphipathic proteins, the membrane scaffold proteins (MSP) derived from the apolipoprotein A-1 [8-10]. Details of the preparation can also be found at http //sligarlab.life.uiuc.edu/nanodisc/protocols.html. These proteins wrap around the hydrophobic core of the lipids, effectively creating a soluble portion of membrane. 

Kalmar, G.B., Kay, R.J., LaChance, A., Aebersold, R., and Cornell, R.B. (1990) Cloning and expression of rat liver CTP phosphocholine cytidylyltransferase an amphipathic protein that controls phosphatidylcholine synthesis, Proc. Natl Acad. Scl USA. 87, 6029-6033. 

Murphy, D.J., Keen, J.N., O Sullivan, J.N., Au, D.M.Y., Edwards, E-W., Jackson, P.J., Cummins, I., Gibbons, T., Shaw, C.H. and Ryan, A.J. (1991) A class of amphipathic proteins associated with lipid storage bodies in plants. Possible similarities with animal serum apolipoproteins. Biochim. Biophys. Acta 1888, 86-94. 

There are three proteins required for the formation of unsaturated fatty acids from precursor saturated acids by the microsomal electron-transport chain. They are NADH-cytochrome reductase, cytochrome 5, and acyl-CoA desaturase. The reaction sequence (Fig. lA) requires molecular oxygen as a proton acceptor, and electrons from NADH. The electron-transport sequence commences with the reductase, passes through cytochrome b, and terminates with the cyanide-sensitive factor, acyl-CoA desaturase (Enoch et al., 1976). Both cytochrome b reductase and cytochrome b are amphipathic proteins in which the redox center is located at the hydrophilic end while the hydrophobic portion binds to lipid moieties (DePierre and Ernster, 1977). Several studies have demonstrated the ability of cytochrome b and cytochrome b reductase to undergo lateral diffusion both in microsomes and in liposomes during the course of electron transfer (Hackenbrock, 1976). 

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