The evolutionary aspects of aquaporin family.

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.

Pressure-dependent hydrogen permeability extended for metal membranes not obeying the square-root law.

Hydrogen permeability of metal membranes is generally defined by the square-root law, as the proportional coefficient of permeation flux to the square-root difference of the pressures on both sides of the membrane. However, deviation from the law has been widely reported for palladium, niobium, etc. Although n-th power instead of the square root has often been employed to determine permeability for these membranes, it has no theoretical base. These approaches do not consider concentration dependency of hydrogen diffusivity in the membrane. This study theoretically extended the definition of permeability by taking it into account, where square root of pressure was used throughout. The resultant permeability depended on pressure. This approach had the following four characteristics. First, the permeability could be qualitatively linked with pressure-dependent solution and diffusion coefficients. For this purpose, the solution coefficient was also extended from Sieverts' law. Second, the permeability could be easily evaluated from permeation flux dependent on feed-side pressure, usually measured in membrane study. Third, this approach enabled comparison of permeation ability irrespective of obeying permeation law. Fourth, permeation flux could be estimated for any pressure conditions visually and analytically. Thus, analytically estimated values were more precise than those using the conventional square-root law. These characteristics are successfully demonstrated using experimental results obtained not only for a palladium membrane in this study but also for palladium and niobium membranes in the literature.

Aquaporin water channels in mammals.

Water channels, aquaporins (AQPs), are a family of small integral plasma membrane proteins that primarily transport water across the plasma membrane. There are 13 members (AQP0-12) in humans. This number is final as the human genome project has been completed. They are divided into three subgroups based on the primary sequences: water selective AQPs (AQP0, 1, 2, 4, 5, 6, 8), aquaglyceroporins (AQP3, 7, 9, 10), and superaquaporins (AQP11, 12). Since no specific inhibitors are yet available, functional roles of AQPs are suggested by AQP null mice and humans. Abnormal water metabolism was shown with AQP1, 2, 3, 4, 5 null mice, especially with AQP2 null mice: fatal at neonate due to diabetes insipidus. Abnormal glycerol transport was shown with AQP3, 7, 9 null mice, although they appeared normal. AQP0 null mice suffer from cataracts, although the pathogenesis is not clear. Unexpectedly, AQP11 null mice die from uremia as a result of polycystic kidneys. Interestingly, AQP6, 8, 10, 12 null mice are almost normal. AQP null humans have been reported with AQP0, 1, 2, 3, 7: only AQP2 null humans show an outstanding phenotype, diabetes insipidus. This review summarizes the current knowledge on all mammalian AQPs and hopefully will stimulate future research in both clinical and basic fields.

The role of a group III AQP, AQP11 in intracellular organelle homeostasis.

AQP11 is a member of a new aquaporin subfamily which includes many aquaporin homologs with low amino acid identities, around 20% of previously identified AQPs. Although these AQPs have unusual NPA sequences, these AQPs have a completely conserved and functionally indispensable cysteine residue downstream of the second NPA box, suggesting that they belong to a specific AQP subfamily, which we propose to name the group III AQPs. On the other hand, the NPA boxes are highly conserved in previous AQP subfamilies: the group I AQPs, original water-selective aquaporin family and the group II AQPs, aquaglyceroporin family. Currently the roles of the group III AQPs are only known with AQP11 as the disruption of intracellularly located AQP11 in mice produced huge vacuoles in the proximal tubule leading to fatal polycystic kidneys at one month old. This review focused on the classification of AQPs based on primary structures to obtain insights into the function and the role of AQPs. With the accumulation of new AQP-like sequences through genome projects, this classification will be useful to predict their functions as each group may have specific characteristics in its function, distribution and regulation.

Controllable growth of well-defined regular multiporphyrin array nanocrystals at the water-chloroform interface.

On the basis of the coordination geometry of metal ions, regular cubic, clubbed, and wirelike nanocrystals of Cd(2+)-/PtCl(6)(2-)-mediated, and Hg(2+)-/Ag(+)-/PtCl(4)(2-)-mediated multiporphyrin arrays have been grown at the water-chloroform interface. The nanocrystal growth process was monitored by the transmission electron microscopy (TEM), which revealed (1) an intrinsic rule for coordination polymers, that is, the geometries of metal ions (as connects for the coordination polymers) dominate the frameworks of the related polymeric nanocrystals, and (2) one kind of intuitive nanocrystal growth processes at the interfaces. Both electron diffraction and X-ray diffraction patterns indicated the formation of well-defined nanocrystals. It was found that single-/microcrystals were formed at first, and then they grew into polycrystals. The nanocrystal layer was transferred onto Si and quartz substrate surfaces by the Langmuir-Blodgett method, with its composition analyzed by X-ray photoelectron spectroscopy as well as the arrangement of porphyrin macrocycles in the nanocrystals by UV-vis absorption spectroscopy.