Aquaporin (AQP2, 12q13, APQ4, 18q11.2-q12.1)

Six transmembrane domain proteins (M_r 28K) and water channel in fluid absorbing and fluid secreting cells. The AQP1 monomer contains 269 amino acids, forming two tandem repeats of three membrane-spanning domains and amino and carboxy termini located on the cytoplasmic side of the membrane. The AQP family includes proteins with wide distribution in diverse species across the plant, animal and microbial world. The aquaporin channel of plants is closed when two conserved serine residues are dephosphorylated or when a conserved histidine is protonated during anoxia by flooding. In closed conformation a D loop caps the channel from the cytoplasm. In open conformation the D loop is displaced and removes the blockade of the entrance of the channel from the cytoplasm (Törnroth-Horsfield S et al 2006 Nature [Lond] 439:688). cAMP-dependent mechanisms or PKA activate the aquaporin channel. It is important for various types of cells, diabetes, kidney function, Drosophilaneural development,...