| Type: | Family | Name: | Aquaporin 1 |
| Description: | Aquaporins are water channels, present in both higher and lower organisms, that belong to the major intrinsic protein family. Most aquaporins are highly selective for water, though some also facilitate the movement of small uncharged molecules such as glycerol []. In higher eukaryotes these proteins play diverse roles in the maintenance of water homeostasis, indicating that membrane water permeability can be regulated independently of solute permeability. In microorganisms however, many of which do not contain aquaporins, they do not appear to play such a broad role. Instead, they assist specific microbial lifestyles within the environment, e.g. they confer protection against freeze-thaw stress and may help maintain water permeability at low temperatures []. The regulation of aquaporins is complex, including transcriptional, post-translational, protein-trafficking and channel-gating mechanisms that are frequently distinct for each family member.Structural studies show that aquaporins are present in the membrane as tetramers, though each monomer contains its own channel [, , ]. The monomer has an overall "hourglass" structure made up of three structural elements: an external vestibule, an internal vestibule, and an extended pore which connects the two vestibules. Substrate selectivity is conferred by two mechanisms. Firstly, the diameter of the pore physically limits the size of molecules that can pass through the channel. Secondly, specific amino acids within the molecule regulate the preference for hydrophobic or hydrophilic substrates.Aquaporin-1 is the major water channel present in the kidney proximal renal tubule. Members of the family contain approximately 275 amino acids. Aquaporin-1 is under complex regulation, including hormones and homeostatic factors like hypertonicity []. It is also expressed in red blood cells, the gastrointestinal tract, lungs and in the brain, where it may have a role in cerebral oedema after surgery or trauma []. Apart from controlling the water balance of the organism [, ], aquaporin-1 is thought to have an impact on various cellular processes, such as angiogenesis, and cell migration and metastasis observed in some human malignancies. Its expression has also been proposed as a characteristic feature of an aggressive sub-group of breast carcinomas. | Short Name: | Aquaporin_1 |
