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From Proteopedia

Revision as of 06:27, 24 April 2015

Aquaporin (AQP) The water channel of the cell

This is a membrane proteins that control the amount of water that travels in and out of the cell. Before the discovery of aquaporin, it was thought that water molecule just leaked through the phospholipid bilayer. Aquaporins allow water to flow rapidly to the inside of cell then it would by crossing the bilayer. This protein is highly selective to water molecules , preventing the passage of ions and other solutes.There are multiple types of aquaporins that can allow the transport of other molecules such as glycerol,CO2, ammonia and urea by aquaglyceroporin. It depends on the size of the pore; aquaporin 3 channel has a pore width of 8-10 Ångströms and allows the passage of hydrophilic molecules ranging between 150-200 Da. Aquaporins water channel are impermeable to protons and other charged species Water molecules traverse through the pore of the channel in single file. The presence of water channels increases membrane permeability to water.

Structure Aquaporin is a six transmembrane alpha helices; the amino and craboxyl terminal are located at the cytoplasm. The protein is divided into two halves of similar sequence. Aquaporin is a tetramer, each monomer is able to channel water. five interhelical loop regions (A – E) Loops B and E are hydrophobic loops which contain the highly, although not completely conserved Asn-Pro-Ala overlap the middle of the lipid bilayer of the membrane forming a 3-D 'hourglass' structure where the water flows through water pores are completely impermeable to charged species, such as protons, a property critical for the conservation of membrane's electrochemical potential.he water molecules move through the narrow channel by orienting themselves in the local electrical field formed by the atoms of the channel wall. Upon entering, the water molecules face with their oxygen atom down the channel. Midstream, they reverse orientation, facing with the oxygen atom up. This rotation of the water molecules in the pore is carried out by the interaction of hydrogen bonds between the oxygen of the water molecule and the asparagines.The narrow pore acts to weaken the hydrogen bonds between the water molecules allowing the water to interact with the positively charged arginine, which also acts as a proton filter for the pore.

Function

The location of Aquaporin is usually found in the kidney, eye and plants. Aquaporin are concentrated in the kidney is h

integral membrane proteins from a larger family of major intrinsic proteins (MIP) A small number of people have been identified with severe or total deficiency in aquaporin-1. Interestingly, they are generally healthy

defect in the ability to concentrate solutes in the urine and to conserve water when deprived of drinking water play a key role in acquired forms of nephrogenic diabetes insipidus (disorders that cause increased urine production

There are thirteen known types of aquaporins in mammals, and six of these are located in the kidney. The most studied aquaporins are AQP1, AQP2, AQP3, and AQP4. . Additionally, it is found in red blood cells, vascular endothelium, the gastrointestinal tract, sweat glands, and lungs. t is found in the basolateral and apical plasma membranes of the proximal tubules, the descending limb of the loop of Henle,

Cite information from websites: http://www.ks.uiuc.edu/Research/aquaporins/ http://www.aquaporins.org/aquaporins/structure.htm