The evolutionary aspects of aquaporin family

Abstract

Aquaporins (AQPs) were originally identified as channels facilitating water transport across the plasma membrane. They have a pair of highly conserved signature sequences, asparagine-proline-alanine (NPA) boxes, to form a pore. However, some have little conserved amino acid sequences around the NPA boxes unclassifiable to two previous AQP subfamilies, classical AQPs and aquaglyceroporins. These will be called unorthodox AQPs in this review. Interestingly, these unorthodox AQPs have a highly conserved cysteine residue downstream of the second NPA box. AQPs also have a diversity of functions: some related to water transport such as fluid secretion, fluid absorption, and cell volume regulation, and the others not directly related to water transport such as cell adhesion, cell migration, cell proliferation, and cell differentiation. Some AQPs even permeate nonionic small molecules, ions, metals, and possibly gasses. AQP gene disruption studies have revealed their physiological roles: water transport in the kidney and exocrine glands, glycerol transport in fat metabolism and in skin moisture, and nutrient uptakes in plants. Furthermore, AQPs are also present at intracellular organelles, including tonoplasts, mitochondria, and the endoplasmic reticulum. This review focuses on the evolutionary aspects of AQPs from bacteria to humans in view of the structural and functional diversities of AQPs.

Homozygosity for aquaporin 7 G264V in three unrelated children with hyperglyceroluria and a mild platelet secretion defect

“…The channel pore is made of two highly conserved short hydrophobic regions with a typical asparagine-prolinealanine (NPA) motif. 6,7 To date, 13 AQP family members (AQP0-12) have been identified in various mammalian tissues. 2 AQPs are classified, according to their sequence homology and permeability, into three subfamilies: (i) the water-specific "classical" AQPs, (ii) the aquaglyceroporins, and (iii) the unorthodox AQPs.…”

“…Unorthodox AQPs are highly similar to the other AQP subclasses, but additional three-dimensional structure analyses are required for a better understanding of the pore structure of this subclass. 7 Aquaporin 7 (AQP7; MIM602974) was previously referred to as "aquaporin adipose" because it was originally identified in human adipose tissue. 12 Subsequently, other researchers found AQP7 expression in testis and renal proximal tubule cells.…”

Cadmium affects osmotic phase and regulatory volume decrease in cultured human embryonic kidney cells

“…Furthermore, both 1 and 10 µM Cd 2+ -treated HEK 293 cells did not exhibit a peak value comparable to that observed in untreated cells. This result provides evidence for an inhibition of OP inhibition presumptively due to aquaporins, 18,34,35 rather than an inhibition of RVD mechanisms, suggesting thus a possible action of the metal on water flux. On the other hand, OP was preserved in 100 µM Cd 2+ -treated HEK 293 cells, while RVD inhibited, suggesting a possible action of the metal on ion transport, namely both K + and Cl -flux, playing a major role in RVD response.…”

<b>Phosphorylation and dephosphorylation of aquaporin-2 at serine 269 and its subcellular distribution during vasopressin-induced exocytosis and subsequent endocytosis in the rat </b><b>kidney </b>

“…To date, 13 AQP isoforms have been identified in mammals (Ishibashi et al, 2011). The mammalian kidney reabsorbs large amounts of water from the glomerular filtrate, which requires at least four AQP isoforms : AQP1, AQP2, AQP3, and AQP4.…”