Membrane channel protein, function

Reizer, J., Reizer, A., and Saier, M. H., Jr. (1993). The MIP family of integral membrane channel proteins sequence comparisons, evolutionary relationships, reconstructed pathway of evolution, and proposed functional differentiation of the two repeated halves of the proteins. Crit. Rev. Biochem. Mol. Biol. 28, 235-257. 

D. JuretiC and B. Lubic, Predicting the secondary structure of membrane channel proteins The performance of preference functions compared to other statistical methods, HB93 Proceedings, Zagreb (1993). 

In contrast to the structure of the K channel, the Cl" channel maintains a large cavity but the ion is surrounded by the positive amino ends (-NH3 ) of peptide chains. The pore channel/filter places amide nitrogen atoms (-CO-NH-) rather than carbonyl oxygen atoms in contact with Cl". The result is to create a low-energy pathway for an anion rather than for a cation through the Cl" membrane channel protein. MacKinnon s group and others are currently involved in studies of the structure and function of the gating mechanism that opens and closes the channel at the intracellular end. 

With the onset of ischemia, there is an influx of sodium, calcium and chloride with the concomitant release of potassium. The movement of the sodium and chloride results in the influx of water and brain swelling (Kimelberg, 2005). The influx of calcium is compounded secondarily by the release of endogenous calcium stores from the endoplasmic reticulum (Phillis et al, 2002). The excessive rise in Ca that results from an ischemia-induced failure of these homeostatic mechanisms represents a non-physiological stimulus that activates a wide array of intracellular receptors, membrane channels, proteins and enzymes, which lead to the compromise of the cell s functional and structural integrity. 

Membrane proteins comprise another important class of protein crystallized in 2D. These proteins perform important functions as membrane channels and recognition sites for cells. Unlike the streptavidin crystals, membrane proteins... 

Chloride channels are membrane proteins that allow for the passive flow of anions across biological membranes. As chloride is the most abundant anion under physiological conditions, these channels are often called chloride channels instead of anion channels, even though other anions (such as iodide or nitrate) may permeate better. As some CLC proteins function as CF-channels, whereas other perform CF/H+-exchangers are also mentioned here. 

While it has been known for many years that the N-terminal presequence is sufficient to promote mitochondrial targeting and assembly, the subsequent interaction of the precursor molecule with the outer mitochondrial membrane and the uptake of the protein is still an area of active research. There seems little doubt, however, that there are proteins on the outer mitochondrial membrane which are required for the import process. The function of these proteins is uncertain, but they may act as receptors with the subsequent transfer through the membrane at proteinous pores located at contact sites between the inner and outer membranes. Several proteins have been identified which seem to play an important role as either receptor proteins or part of the import channel (Pfanner et al., 1991). Again, not all proteins seem to depend on this mechanism. Cytochrome c, which is loosely associated with the outer aspect of the inner mitochondrial membrane, can cross... 

The common denominator of all these CP-channel blockers (Fig. 2) is their acidic function (usually carboxylate), the secondary amine with a certain spacing to the acidic group, a nitro substitution at a certain distance from the carboxylate group, and the apolar groups such as the phenyl-propyl-residue. We have suggested that the interaction with the CP-channel requires all of these interaction sites, and that even the apolar moiety of the blocker molecule reacts with the channel protein rather than with the membrane lipid [70]. 

The majority of cases of cystic fibrosis result from deletion of phenylalanine at position 508 (AF508), which interferes with proper protein folding and the posttranslational processing of oligosaccharide side chains. The abnormal chloride channel protein (CFTR) is degraded by the cytosolic proteasome complex rather than being translocated to the cell membrane. Other functional defects in CFTR protein that teaches the cell membrane may also contribute to the pathogenesis of cystic fibrosis. 

Figure 2.2 Diagram of a voltage-activated sodium channel protein. The channel is composed of a long chain of amino acids intercormected by peptide bonds. The amino acids perform specific functions within the ion channel. The cylinders represent amino acid assemblies located within the membrane of the nerve cell and responsible for the foundation of the ion pore.

VirB proteins in the secretion system most form the membrane channel or serve as ATPases to provide energy for channel assembly or for export processes. Several of these VirB proteins form the T-pilus. The function of the T-pilus remains unclear it may be required as the channel for T-DNA and Vir protein transfer, or it may act as a hook to grab hold of the recipient host cell and bring plant and bacterium close together for efficient gene transfer (Gelvin, 2003, LaCroix et ah, 2006a). 

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