Aquaporin

Aquaporins are a class of integral membrane proteins that form pores in the membrane of biological cells and selectively conduct water molecules in and out, while preventing the passage of ions and other solutes. Also known as water channels, they are each composed of four (typically) identical subunit proteins. Water molecules traverse the narrowest portion of the channel single file. The presence of water channels increases the permitivity of membranes to water by as much as ten fold. Many human cell types express them, as do certain bacteria and many other organisms. Genetic defects involving aquaporin genes have been associated with several human diseases.

External References

http://www.ks.uiuc.edu/Research/aquaporins/ Animation[1]\n