Structural insights into eukaryotic aquaporin regulation

Törnroth-Horsefield, Susanna; Hedfalk, Kristina; Fischer, Gerhard W.; Lindkvist‐Petersson, Karin; Neutze, Richard

doi:10.1016/j.febslet.2010.04.037

Cited by 142 publications

(127 citation statements)

References 94 publications

(202 reference statements)

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“…For the case of AQY1, its crystal structure revealed that the water channel was regulated by gating (45), and it was suggested that reconstitution of AQY1 into proteoliposomes, which have a FIGURE 4. CD spectra and melting curves, demonstrating the stability of hAQP10.…”

Section: Discussionmentioning

confidence: 99%

Glycosylation Increases the Thermostability of Human Aquaporin 10 Protein

Öberg

Sjöhamn

Fischer

et al. 2011

Journal of Biological Chemistry

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Human aquaporin10 (hAQP10) is a transmembrane facilitator of both water and glycerol transport in the small intestine. This aquaglyceroporin is located in the apical membrane of enterocytes and is believed to contribute to the passage of water and glycerol through these intestinal absorptive cells. Here we overproduced hAQP10 in the yeast Pichia pastoris and observed that the protein is glycosylated at Asn-133 in the extracellular loop C. This finding confirms one of three predicted glycosylation sites for hAQP10, and its glycosylation is unique for the human aquaporins overproduced in this host. Nonglycosylated protein was isolated using both glycan affinity chromatography and through mutating asparagine 133 to a glutamine. All three forms of hAQP10 where found to facilitate the transport of water, glycerol, erythritol, and xylitol, and glycosylation had little effect on functionality. In contrast, glycosylated hAQP10 showed increased thermostability of 3-6°C compared with the nonglycosylated protein, suggesting a stabilizing effect of the N-linked glycan. Because only one third of hAQP10 was glycosylated yet the thermostability titration was mono-modal, we suggest that the presence of at least one glycosylated protein within each tetramer is sufficient to convey an enhanced structural stability to the remaining hAQP10 protomers of the tetramer.Intrinsic membrane proteins are essential for the selective transport of molecules in and out of cells and hence the regulation of their concentration within the cell. Aquaporins (AQPs) 2 primarily facilitate the transport of water across biological membranes, where water movements are driven by hypertonic or hypotonic conditions. AQPs consist of six transmembrane domains and five connecting loops ( Fig. 1) with both termini located on the intracellular side of the membrane. Aquaporins also contain two half-helices in loops B and E which align to form a pseudo-transmembrane helix, the focus of which contains the signature motif asparagine-proline-alanine (NPA). In vivo the protein assemblies into homotetramers, and each monomer functions as a water channel. Thirteen aquaporin family members exist within humans, with varying tissue distribution and substrate specificity (1). Two major subclasses have been identified: the orthodox aquaporins (hAQP0, hAQP1, hAQP2, hAQP4, hAQP5, hAQP6, and hAQP8) mainly facilitating the movement of water, and the aquaglyceroporins (hAQP3, hAQP7, hAQP9, and hAQP10) which facilitate both the transport of water and of other small solutes.Human aquaporin10 (hAQP10) was first identified in a human jejunum cDNA library and was observed to have 264 amino acids and dual copies of the aquaporin signature NPA motifs, confirming it as a member of the aquaporin family located in the small intestine (2). From homology studies the protein had been classified as an aquaglyceroporin, but surprisingly it did not show any glycerol or urea transport and only a low permeability to water in Xenopus oocytes (2). Shortly thereafter, an independent study identified...

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Section: Discussionmentioning

confidence: 99%

Glycosylation Increases the Thermostability of Human Aquaporin 10 Protein

Öberg

Sjöhamn

Fischer

et al. 2011

Journal of Biological Chemistry

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“…However, despite the fact that ovaries from water-stressed specimens started basal oocyte resorption 48h after water deprivation, no significant differences were observed in the levels of BgAQP mRNA in the ovary between control and water-stressed specimens. AQPs are regulated post-translationally by phosphorylation-dependent gating and especially by trafficking of the protein between the plasma membrane and the intracellular storage vesicle (Törnroth-Horsefield et al, 2010); thus, the effects of water stress on BgAQP may not be evident at the mRNA level.…”

Section: A Herraiz and Othersmentioning

confidence: 99%

“…In the cell membrane, each AQP is folded into a right-handed -barrel, with a central transmembrane channel surrounded by the six full-length transmembrane helices and the two NPA-containing loops, B and E. This conformation in the plasma membrane is known as the hourglass model (Jung et al, 1994). Some AQPs, known as aquaglyceroporins, transport other non-charged solutes such as glycerol and urea in addition to water (Gomes et al, 2009;Rojek et al, 2008;Törnroth-Horsefield et al, 2010). The amino acids forming the ar/R constriction (His is replaced by the smaller amino acid Gly in aquaglyceroporins) (Beitz et al, 2006), and five other residues (P1-P5) located on the side-chains neighbouring the ar/R constriction (Froger et al, 1998), are responsible for substrate selectivity.…”

Section: Introductionmentioning

confidence: 99%

Identification and functional characterization of an ovarian aquaporin from the cockroachBlattella germanicaL. (Dictyoptera, Blattellidae)

Herraiz

Chauvigné

Cerdà

et al. 2011

Journal of Experimental Biology

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SUMMARYAquaporins (AQPs) are membrane proteins that form water channels, allowing rapid movement of water across cell membranes. AQPs have been reported in species of all life kingdoms and in almost all tissues, but little is known about them in insects. Our purpose was to explore the occurrence of AQPs in the ovary of the phylogenetically basal insect Blattella germanica (L.) and to study their possible role in fluid homeostasis during oogenesis. We isolated an ovarian AQP from B. germanica (BgAQP) that has a deduced amino acid sequence showing six potential transmembrane domains, two NPA motifs and an ar/R constriction region, which are typical features of the AQP family. Phylogenetic analyses indicated that BgAQP belongs to the PRIP group of insect AQPs, previously suggested to be water specific. However, ectopic expression of BgAQP in Xenopus laevis oocytes demonstrated that this AQP transports water and modest amounts of urea, but not glycerol, which suggests that the PRIP group of insect AQPs may have heterogeneous solute preferences. BgAQP was shown to be highly expressed in the ovary, followed by the fat body and muscle tissues, but water stress did not significantly modify the ovarian expression levels. RNA interference (RNAi) reduced BgAQP mRNA levels in the ovary but the oocytes developed normally. The absence of an apparent ovarian phenotype after BgAQP RNAi suggests that other functionally redundant AQPs that were not silenced in our experiments might exist in the ovary of B. germanica. Supplementary material available online at

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“…In addition to their wellestablished water-and glycerol-transporting functions, AQPs have also been proposed to transport other small molecules and gases, including carbon dioxide, ammonia, nitric oxide and hydrogen peroxide (Musa-Aziz et al, 2009;Miller et al, 2010;Wang and Tajkhorshid, 2010). Although some gases are theoretically small enough to pass through the aqueous pore of the AQP, compelling evidence is lacking for physiologically relevant gas transport, partly because the intrinsic lipid-mediated membrane permeability to most gases is high (Yang et al, 2000;Missner et al, 2008;Tornroth-Horsefield et al, 2010). Current evidence suggests that most, if not all, significant biological functions of the mammalian AQPs, including those described here, can be attributed to AQPfacilitated water and/or glycerol transport.…”

Section: Aqp Structure Function and Regulationmentioning

confidence: 99%