Gjb2 Protein In Gap Junction

Cystic fibrosis (CF) is a progressive condition in which epithelial exocrine glands are obstructed (Howe, 2001). Whilst many organs and bodily systems are disrupted by CF, the lungs and gastrointestinal organs are predominantly affected; it is also most common amongst the Caucasian population due to the autosomal recessive gene (Quitter et al., 2003 cited in Wolfe & Mash, 2006, pg 514). The faulty gene effects the production of cystic fibrosis transmembrane conductance regulator protein, which is responsible for the formation of molecular tunnels which monitor the movement of salts and water from the cells (Hopkin, 2010 pg 4).

A. Connexons containing p.Gly45Glu mutants function as hemichannels with aberrantly increased activity that leads to the disease manifestations. Gly45 locates at a domain that lines the channel pore and probably mediates voltage sensing. Cx26 carrying p.Gly45Glu/p.Tyr136X alteration would be excluded from the hexameric connexons, a second-site mutation cancels an exsisting pathogenic mutation.

In the special case of CFTR, a single gene codes for 5 domains of the 1480 amino acid glycoprotein, but homologous halves are linked by a unique regulatory domain (R) that acts as the binding site for PKA giving the domain conformation of CFTR as TMD1-NBD1-R-NBD2-TMD2 (Gadsby et al., 2006). For the movement of ions across the membrane, negatively charged ions, like chloride, accrue near the positively charged ends of the 2 TMDs. The flow of these ions occurs down their electrochemical gradient when the channel opens up (Linsdell, 2005). However, for this to occur, PKA must first phosphorylate the R domain, to allow for the binding of ATP to the NBDs, nestled within a Walker A motif. Once this occurs, the 2 NBDs dimerize causing a power stroke that brings on the conformational change of the 2 TMDs and the opening of the chloride channel allowing for the flow of ions. This conformational change is sustained until hydrolysis of one the ATPs occurs (Furukawa-Hagiya et al., 2013). A graph showing the importance of PKA in CFTR opening and the general mechanism of the channel opening can be observed in figure-1.

During one open-close cycle, ATP binds to the first site NBD1 and is hydrolyzed, this release of energy opens the MSDs pore, allowing active transport of the chloride ion through the cell membrane. Then a second ATP is bound NBD2 and hydrolyzed charging the closure of the channel (Gadsby & Nairn, 1999). Lastly, at the R-domain, the phosphatases protein returns the channel to its inactive state (Sheppard & Welsh, 1999).

As has been discussed, an inheritable mutation in genes coding for the beta and gamma subunits of the ENaC, causing deletion or truncation of the PY motif leads to a disruption in ENaC ubiquitination. Ubiquitination itself is the process of tagging a protein with a series of glycosyl subunits, signalling its degradation at the proteasome, destroying the channel. With this inhibition in ubiquitination, ENaC is expected to and is seen to have a much larger surface expression and channel open probability, leading to an overall increase in sodium reabsorption which causes the characteristic symptoms of Liddle’s syndrome. Through understanding the two major regulatory mechanisms at the levels of protein trafficking of the ion channel and protein-protein interactions with the channel itself, better methods of control and a better understanding of Liddle’s syndrome can be

Stemming from a genetic mutation with a membrane pore, or channel that helps to facilitate the transport of bicarbonate electrolytes and chloride from between the inside and the outside of the cell, cystic fibrosis and its inherent symptoms are caused by the loss of the pore channel, which results in inflammation and mucus accumulation. Dehydration of the cell surface also occurs. Normally, cells have a cystic fibrosis transmembrane regulator channel that influences fluid secretion in epithelial cells. When this channel is mutated, there is a decrease in the flow of ions and water, and this results in dehydrated mucous that affects breathing. This in turn causes lethal bacterial infections by blocking ducts within the lungs. The most common mutation of the cystic fibrosis conductance regulator is F508del-CFTR. This mutation creates a misprocessed protein that rapidly degrades as it is abnormally retained in the endoplasmic reticulum compartment, therefore making it absent in the plasma membrane

Chloride channels are a structurally diverse superfamily of transmembrane proteins that facilitate the transport of negative anions across the cell membrane. These channels are involved in a plethora of physiological processes such as neurotransmission, excitation of skeletal, cardiac, and smooth muscle, salt transport, cell volume regulation, and acid production in internal and external compartments. Families of these channels include the voltage-gated CLC family, calcium-activated CaCC family, GABAA receptors, glycine receptors, and the cystic fibrosis transmembrane conductance regulator (CFTR). CFTR is an ATP-binding cassette (ABC) transporter that is responsible for proper fluid transport across the epithelial membrane of various cells within body tissues such as the lungs, liver, digestive tract, and reproductive tract. Mutations in the protein sequence of CFTR are characteristic of the disease cystic fibrosis, a disease where improper or absent ion movement decreases the flow of water across exocrine epithelial cells causing mucus and other secretions to be unusually thick.

Brain is the most complex organ in the human body. Brain and spinal cord made up part of the nervous system called central nervous system (CNS). The cerebral cortex which is the largest part of human brain has more than 100 billion of neurones, and each connected by synapses that communicate to other neurons (Pelvig DP, et al., 2008). There are several types of ion channels present along the neurons, one of these is potassium channels. Potassium channels are the integral membrane proteins that span through phospholipids bilayer of cell surface membrane which rapidly conduct potassium ions down their electrochemical gradient (Mark S.P. Sansom, et al., 2002). There are many forms of potassium channels with different functional properties. Therefore, how the tremendous diversity of potassium channels contribute well to the biological process in brain? It is vital for us to understand the important of potassium channel diversity and know benefits for the existence of the potassium channels diversity in the brain?

Maxi-K channels consist of a pore-forming α subunit and a regulatory β subunit. Maxi-K channels are of a high Ca2+ sensitivity [2].

Tong, B., Hornak, A., Maison, S., Ohlemiller, M., Liberman, M., Simmons, D. (2016). Oncomodulin, an EF-Hand Ca2+ Buffer, Is Critical for Maintaining Cochlear Function in Mice. Journal of Neuroscience. 36 (5) 1631-1635.

Cystic fibrosis is the most common autosomal recessive disorder in Caucasian’s with an incidence rate of 1 in every 2,500 births. Cystic Fibrosis, commonly known as CF, is a life-threatening, lethal genetic disease that mostly affects the lungs and digestive system (O’Sullivan & Freedman, 2009). An individual with cystic fibrosis has a specific mutation in a gene and protein called cystic fibrosis transmembrane conductance regulator (CFTR). This protein acts as a channel for ions, which help the body in healthy balance of salt and water. An individual with this mutation of CFTR creates sticky, thick mucus (Falvo, 2014 p. 486). This abnormal mucus affects individuals with CF by forming blockage in their respiratory track and obstruction in his or her pancreases (Ratjen & Doring, 2003).

As previously described, gap junction channels allow the delivery of signals from one cell to another. These cell signals can be for cell survival or cell death. The effect where neighboring cells are affected through the spread of GJP is known as the bystander effect.

16) Tight junctions prevent leaking in fluids. Anchoring junctions are common in tissues to stretching and mechanical stress. Gap junctions allow small molecules to flow through pores in cells.

The gene GJB3 (gap junction beta-3) encodes the protein Connexin 31. Connexin 31 is a member of the connexin gene family. Connexins are four-pass transmembrane proteins with both C and N cytoplasmic termini, a cytoplasmic loop (CL) and two extra-cellular loops, (EL-1) and (EL-2). Connexins are a group of proteins that form channels (gap junctions) on the surface of cells. Gap junctions allow direct intercellular communication of low molecular weight substances. Gap junctions open and close to regulate the flow of nutrients, charged atoms (ions), and other signaling molecules from cell to cell. Connexin 31 is found in several different parts of the body, including the outermost layer of the skin (the epidermis). The importance of Cx31

Moreover, in pulmonary artery smooth muscle, Ca2+/CaM-dependent protein kinase II (CaMKII) is associated with CaCCs inhibition 82. The same study has shown that using the inhibitors of CaMKII promotes the amplitude and the opening probability of CaCCs. However, while multiple phosphorylation sites for different kinases such as protein kinases A, protein kinases C, protein kinases G, CaMKII, and casein kinase have been proposed on the mammalian CaCCs sequence, particularly two intracellular sites for extracellular signal–regulated kinase (ERK) have been identified on the C-termini side of the channel 83, ANO1 activity, amplitude, and its opening probability are not remarkably affected by different kinases inhibitors 64. Taken all together, one should consider tissue-specific markers in analyzing the regulatory mechanisms of CaCCs based on different residues located inside or outside of the cell. The six cysteine residues, for instance, located on the extracellular side of the channel have been shown to play a role in chloride current across the channel 84 and hence can be of great value in terms of channel regulation. Furthermore, similar to other ion channels that interact with the cytoskeleton, ANO1 has interactions with ezrin–radixin–moesin (ERM) network of actin-binding