Aquaporins (AQPs) ”water pore” are membrane proteins that function as water-specific channels. A representation of the 3D structure of myoglobin, showing coloured alpha helices. ...

History

Due to the relatively high osmotic permeability of some epithelial cells it was long suspected that some additional mechanism for water transport across the membrane must exist, but it was not until 1992 that the functional characterisation of the first aquaporin, ‘aquaporin-1’, was reported. The pioneering discoveries and research into water channels by Peter Agre and Roderick MacKinnon resulted in their claiming the 2003 Nobel Prize in Chemistry. In 2000, together with other research teams, Agre reported the first high-resolution images of the three-dimensional structure of the aquaporin. Further studies using supercomputer simulations have produced a probable mechanism of the action of aquaporin channels. In zootomy, epithelium is a tissue composed of a layer of cells. ... Sir Edward Appletons medal Photographs of Nobel Prize Medals. ... We use computer to go on the porn site ...

Structure

Aquaporins form tetramers in the cell membrane, and facilitate the transport of water and, in some cases, other small solutes, such as glycerol, across the membrane. However, the water pores are completely impermeable to charged species, such as protons, a property critical for the conservation of membrane's electrochemical potential. The aquaporins are predicted to have six membrane-spanning segments, existing in the plasma membrane as homotetramers. Each aquaporin monomer contains two hemi-pores, which fold together to form a water channel ... For alternative meanings see proton (disambiguation). ... Electrochemical potential is a thermodynamic measure that reflects energy from entropy and electrostatics and is typically invoked in molecular processes that involve diffusion. ...

Using computer simulations it has been suggested that the orientation of the water molecules moving through the channel assures that only water passes between cells, due to the formation of a single line of water molecules. The 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. While passing through the channel, the single-file chain of water molecules streams through, always entering face down and leaving face up. The strictly opposite orientations of the water molecules keep them from conducting protons (or rather oxonium ions, H3O+), while still permitting a fast flux of water molecules . General Name, Symbol, Number oxygen, O, 8 Chemical series nonmetals Group, Period, Block 16, 2, p Appearance colorless Atomic mass 15. ... For alternative meanings see proton (disambiguation). ...

Aquaporins in mammals

Water crosses the cell membrane by either diffusing through the phospholipid bilayer or by passing through special water channels called aquaporins. More than 10 mammalian aquaporins have so far been identified, but the existence of many more is suspected. Most aquaporins appear to be exclusive water channels that will not allow permeation of ions or other small molecules. Some aquaporins - known as aquaglyceroporins - transport water plus glycerol and a few other small molecules. A DPPC bilayer simulation Color scheme: PO4 = green, N(CH3)3 = violet, water = blue, terminal CH3 = yellow, O = red, glycol C = brown, chain C = grey In biology and chemistry, a lipid bilayer is a membrane or zone of membrane composed only of lipid. ...

Aquaporins in plants

In plants water is taken up from the soil through the roots, where it passes from the cortex into the vascular tissues. There are two routes for water to flow in these tissues, known as the; apoplastic and symplastic pathways. The presence of aquaporins in the cell membranes seems to serve to facilitate the transcelluar symplastic pathway for water transport. When plant roots are exposed to mercuric chloride, which is known to inhibit aquaporins, the flow of water is greatly reduced while the flow of ions is not, supporting the view that there exists a mechanism for water transport independent of the transport of ions; aquaporins. Apoplast and symplast are two related concepts in plant biology. ... Apoplast and symplast are two related concept in plant biology. ...

Aquaporins and Disease

There have been two clear examples of disease identified as resulting from deficiency in aquaporins:

• Mutations in the aquaporin-2 gene cause hereditary nephrogenic diabetes insipidus in humans.
• Mice homozygous for inactivating mutations in the aquaporin-0 gene develop congenital cataracts.

A small number of people have been identified with severe or total deficiency in aquaporin-1. Interestingly, they appear clinically unaffected, but have not been examined under conditions of water deprivation. Mice with targeted deletions in aquaporin-1 also appear normal and healthy unless they are fluid restricted, in which case they become severely hyperosmolar. This stylistic schematic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). ... Diabetes without a modifier usually refers to diabetes mellitus. ... Homozygote cells are diploid or polyploid and have the same alleles at a locus (position) on homologous chromosomes. ...

References

• R. Bowen, Colorado State University, January 2, 2002

• Nobel Museum

• Department of Biology, University of Miami, Coral Gables

• Niall Harrison