Aquaporin Family Research Articles

Relative CO 2 /NH 3 permeabilities of several members of the mammalian Aquaporin family: bAQP0, hAQP1, hAQP2, rAQP3, rAQP4‐M1, rAQP4‐M23, and hAQP8

The mammalian aquaporins (AQPs) have 13 members in two major families, the orthodox AQPs and the aquaglyceroporins, which also transport glycerol and other small solutes. Previously, we showed that human (h) AQP1, rat (r) AQP4-M23, and rAQP5—abundantly expressed in cells with high rates of gas transport—exhibit selectivity for CO2 over NH3 (AQP4-M23 ≅ AQP5 > AQP1). Here we extend this analysis to: bAQP0, hAQP1 (repeated), hAQP2, rAQP3, rAQP4-M1, rAQP4-M23 (repeated), and hAQP8. We expressed the AQPs in Xenopus oocytes and used microelectrodes to record the maximum transient change in surface pH (ΔpHS) caused by exposure to extracellular CO2 (an increase) or NH3 (a decrease). We computed osmotic water permeability (Pf) from rates of cell swelling under hypotonic conditions. Subtracting the respective values for day-matched, H2O-injected control oocytes yielded channel-specific values (*). (ΔpHS*)CO2 was significantly different from 0 only for: AQP0, AQP1, and AQP4-M23. (−ΔpHS*)NH3 was significantly different from 0 only for: AQP1, AQP3, and AQP8. Pf* was significantly different from 0 for all tested AQPs. The ratio (ΔpHS*)CO2/Pf* fell in the sequence: hAQP1 > AQP4-M23 > AQP0 > [AQP2 ≅ AQP3 ≅ AQP4-M1 ≅ AQP8 = 0]. The ratio (ΔpHS*)CO2/(−ΔpHS*)NH3 fell in the sequence: [AQP0 ≅ AQP4-M23 = infinity] > AQP1 > [AQP3 ≅ AQP8 = 0]. Thus, this group of AQPs exhibits a diverse range of selectivities for CO2 vs NH3 vs H2O.

Patterns of aquaporin expression in the canine eye

Aquaporins (AQPs) function as water channels in many types of cells involved in fluid transport. More than 10 isoforms have been identified, and these are differentially expressed in many types of mammalian cells in the body. Six AQPs (AQP0, AQP1, AQP3, AQP4, AQP5, and AQP9) have been identified in the eyes of humans and/or rodents. The unique permeability characteristics and distribution of AQPs indicate their diverse roles in the regulation of water homeostasis in the eye. The aim of this study was to investigate the localisation of AQPs in normal canine eyes, with AQP0 protein expressed in the crystalline lens and retina. Although AQP1 mRNA was detected in various areas of the canine eye, its protein expression was limited to the cornea, iris and ciliary body. AQP4 was identified in the iris, retina and optic nerve. AQP3 and AQP5 were found in the cornea and conjunctiva, and their expression was particularly high in the limbus. AQP3 and AQP5 were present in the nictitating membrane indicating that they play a role in water transport within the membrane. The observations suggested that several subtypes of the AQP family are involved in the regulation of water homeostasis in the canine eye.

Mechanisms of cell polarity and aquaporin sorting in the nephron

The kidneys participate in whole-body homeostasis, regulating acid-base balance, electrolyte concentrations, extracellular fluid volume, and regulation of blood pressure. Many of the kidney's functions are accomplished by relatively simple mechanisms of filtration, reabsorption, and secretion, which take place in the nephron. The kidneys generate 140-180 l of primary urine per day, while reabsorbing a large percentage, allowing for only the excretion of approximately 2 l of urine. Within the nephron, the majority of the filtered water and solutes are reabsorbed. This is mainly facilitated by specialized transporters and channels which are localized at different segments of the nephron and asymmetrically localized within the polarized epithelial cells. The asymmetric localization of these transporters and channels is essential for the physiological tasks of the renal tissues. One family of these proteins are the water-permeable aquaporins which are selectively expressed in cells along the nephron and localized at different compartments. Here, we discuss potential molecular links between mechanisms involved in the establishment of cell polarity and the members of the aquaporin family. In the first part of this review, we will focus on aspects of apical cell polarity. In the second part, we will review the motifs identified so far that are involved in aquaporin sorting and point out potential molecular links.

Structure and Stability of the Spinach Aquaporin SoPIP2;1 in Detergent Micelles and Lipid Membranes

BackgroundSoPIP2;1 constitutes one of the major integral proteins in spinach leaf plasma membranes and belongs to the aquaporin family. SoPIP2;1 is a highly permeable and selective water channel that has been successfully overexpressed and purified with high yields. In order to optimize reconstitution of the purified protein into biomimetic systems, we have here for the first time characterized the structural stability of SoPIP2;1.Methodology/Principal FindingWe have characterized the protein structural stability after purification and after reconstitution into detergent micelles and proteoliposomes using circular dichroism and fluorescence spectroscopy techniques. The structure of SoPIP2;1 was analyzed either with the protein solubilized with octyl-β-D-glucopyranoside (OG) or reconstituted into lipid membranes formed by E. coli lipids, diphytanoylphosphatidylcholine (DPhPC), or reconstituted into lipid membranes formed from mixtures of 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPE), 1-palmitoyl-2oleoyl-phosphatidylethanolamine (POPE), 1-palmitoyl-2-oleoyl-phosphatidylserine (POPS), and ergosterol. Generally, SoPIP2;1 secondary structure was found to be predominantly α-helical in accordance with crystallographic data. The protein has a high thermal structural stability in detergent solutions, with an irreversible thermal unfolding occurring at a melting temperature of 58°C. Incorporation of the protein into lipid membranes increases the structural stability as evidenced by an increased melting temperature of up to 70°C.Conclusion/SignificanceThe results of this study provide insights into SoPIP2;1 stability in various host membranes and suggest suitable choices of detergent and lipid composition for reconstitution of SoPIP2;1 into biomimetic membranes for biotechnological applications.

Differential expression of inwardly rectifying K+ channels and aquaporins 4 and 5 in autoimmune uveitis indicates misbalance in Müller glial cell‐dependent ion and water homeostasis

Reactive gliosis is a well-established response to virtually every retinal disease. Autoimmune uveitis, a sight threatening disease, is characterized by recurrent relapses through autoaggressive T-cells. The purpose of this study was to assess retinal Müller glial cell function in equine recurrent uveitis (ERU), a spontaneous disease model resembling the human disease, by investigating membrane proteins implicated in ion and water homeostasis. We found that Kir2.1 was highly expressed in diseased retinas, whereas Kir4.1 was downregulated in comparison to controls. Distribution of Kir2.1 appeared Müller cell associated in controls, whereas staining of cell somata in the inner nuclear layer was observed in uveitis. In contrast to other subunits, Kir4.1 was evenly expressed along equine Müller cells, whereas in ERU, Kir4.1 almost disappeared from Müller cells. Hence, we suggest a different mechanism for potassium buffering in the avascular equine retina and, moreover, an impairment in uveitis. Uveitic retinas showed significantly increased expression of AQP4 as well as a displaced expression from Müller cells in healthy specimens to an intense circular expression pattern in the outer nuclear layer in ERU cases. Most interestingly, we detected the aquaporin family member protein AQP5 to be expressed in Müller cells with strong enrichments in Müller cell secondary processes. This finding indicates that fluid regulation within the equine retina may be achieved by an additional aquaporin. Furthermore, AQP5 was significantly decreased in uveitis. We conclude that the Müller cell response in autoimmune uveitis implies considerable changes in its potassium and water physiology.

Comparative Neural Network and Alignment Study of Aquaporins

Common for the membrane channel protein family of aquaporins is that they facilitate a rapid transport of water molecules. Aquaporins are found in a wide range of organisms and several protein structures have been solved. Although they share structural similarities there are also distinct features for each class (e.g. plant versus mammalian aquaporins). This raises the question: How well does sequence and structural features of the respective proteins correlate to functional sites? We here present a comparative study of aquaporins based on neural network analysis as well as structure, sequence and residue alignments. Using HotPatch, an automated algorithm developed by Pettit et al. (Pettit, F. K. et al. J. Mol. Biol. 2007 369, 863-879) we calculated probable aquaporin functional interaction sites such as sites involved in (specific) lipid interactions. Alignment of the calculated sequences allowed us to analyze similarities and differences in the proteins in a quantitative manner as well as elucidating the potential functional role of specific residues. This will further give us new information on functionally important features that could assist in the design of proteins with increased stability for biomimetic applications.

Multiscale Simulations of Lipid Interactions with Integral Membrane Proteins: Aquaporins

Membrane protein structural biology is one of the key biochemical challenges of the coming decade. With continuous improvements to the methods used by structural biologists there is a predicted exponential growth in the number of membrane proteins structures. Nevertheless, these biological assemblies are usually resolved in the absence of the native lipid environment. Coarse-Grained molecular dynamics (CGMD) simulations provide a means for assessing the assembly and interactions of molecular complexes at a reduced level of representation. This method has been shown to accurately predict the insertion position of proteins within a cell membrane. Previous studies enabled us to correlate predicted contacts to lipids with experimental data on lipid-exposed residues for a number of membrane proteins (e.g. LacY, rhodopsin, KcsA, MscL, FepA, BtuB). The recent determination of high resolution structures for aquaporins in a phospholipid bilayer environment (Aqp0: 2B6O and 3M9I; Aqp4: 2ZZ9) has provided an excellent test case. The CGMD approach has been used to simulate lipid/protein interactions for >30 members of the aquaporin family, revealing that patterns of protein/lipid headgroup interactions are conserved and are in good agreement with the lipids resolved in the electron crystallography structures. We have extended this further by using a multi-scale approach, investigating the interactions at atomic resolution. At this scale we may also consider hydrogen bonding interactions, which also show good agreement with the experimental structures. This methodology is being incorporated into a semi-automated high-throughput pipeline to enrich our database of CGMD membrane protein simulations (CGDB; http://sbcb.bioch.ox.ac.uk/cgdb).

Requirement for asparagine in the aquaporin NPA sequence signature motifs for cation exclusion

Two highly conserved NPA motifs are a hallmark of the aquaporin (AQP) family. The NPA triplets form N-terminal helix capping structures with the Asn side chains located in the centre of the water or solute-conducting channel, and are considered to play an important role in AQP selectivity. Although another AQP selectivity filter site, the aromatic/Arg (ar/R) constriction, has been well characterized by mutational analysis, experimental data concerning the NPA region--in particular, the Asn position--is missing. Here, we report on the cloning and mutational analysis of a novel aquaglyceroporin carrying one SPA motif instead of the NPA motif from Burkholderia cenocepacia, an epidemic pathogen of cystic fibrosis patients. Of 1357 AQP sequences deposited in RefSeq, we identified only 15 with an Asn exchange. Using direct and phenotypic permeability assays, we found that Asn and Ser are freely interchangeable at both NPA sites without affecting protein expression or water, glycerol and methylamine permeability. However, other mutations in the NPA region led to reduced permeability (S186C and S186D), to nonfunctional channels (N64D), or even to lack of protein expression (S186A and S186T). Using electrophysiology, we found that an analogous mammalian AQP1 N76S mutant excluded protons and potassium ions, but leaked sodium ions, providing an argument for the overwhelming prevalence of Asn over other amino acids. We conclude that, at the first position in the NPA motifs, only Asn provides efficient helix cap stabilization and cation exclusion, whereas other small residues compromise structural stability or cation exclusion but not necessarily water and solute permeability.

Large-scale phosphoproteomic analysis of membrane proteins in renal proximal and distal tubule

Recent advances in mass spectrometry (MS) have provided means for large-scale phosphoproteomic profiling of specific tissues. Here, we report results from large-scale tandem MS [liquid chromatography (LC)-MS/MS]-based phosphoproteomic profiling of biochemically isolated membranes from the renal cortex, with focus on transporters and regulatory proteins. Data sets were filtered (by target-decoy analysis) to limit false-positive identifications to <2%. A total of 7,125 unique nonphosphorylated and 743 unique phosphorylated peptides were identified. Among the phosphopeptides identified were sites on transporter proteins, i.e., solute carrier (Slc, n = 63), ATP-binding cassette (Abc, n = 4), and aquaporin (Aqp, n = 3) family proteins. Database searches reveal that a majority of the phosphorylation sites identified in transporter proteins were previously unreported. Most of the Slc family proteins are apical or basolateral transporters expressed in proximal tubule cells, including proteins known to mediate transport of glucose, amino acids, organic ions, and inorganic ions. In addition, we identified potentially important phosphorylation sites for transport proteins from distal nephron segments, including the bumetanide-sensitive Na-K-2Cl cotransporter (Slc12a1 or NKCC2) at Ser(87), Thr(101), and Ser(126) and the thiazide-sensitive Na-Cl cotransporter (Slc12a3 or NCC) at Ser(71) and Ser(124). A subset of phosphorylation sites in regulatory proteins coincided with known functional motifs, suggesting specific regulatory roles. An online database from this study (http://dir.nhlbi.nih.gov/papers/lkem/rcmpd/) provides a resource for future studies of transporter regulation.

Transport of silicon from roots to panicles in plants

Silicon (Si) is the most abundant minerals in soil and exerts beneficial effects on plant growth by alleviating various stresses. The transport of Si from soil to the panicles is mediated by different transporters. Lsi1, belonging to a NIP group of the aquaporin family, is responsible for the uptake of Si from soil into the root cells in both dicots and monocots although its expression patterns and cellular localization differ with plant species. The subsequent transport of Si out of the root cells towards the stele is medicated by an active efflux transporter, Lsi2. Lsi1 and Lsi2 are polarly localized at the distal and proximal sides, respectively, of both exodermis and endodermis in rice root. Silicon in the xylem sap is presented in the form of monosilicic acid and is unloaded by Lsi6, a homolog of Lsi1 in rice. Lsi6 is also involved in the inter-vascular transfer of Si at the node, which is necessary for preferential Si distribution to the panicles.

Aquaporin Membrane Channels: Biophysics, Classification, Functions, and Possible Biotechnological Applications

Water represents the major component of all living organisms. To make the cell to adapt to the surrounding environment and carry out its biological functions, water has to move into and out of the cell interior driven by osmotic forces. For over a century, scientists studying the movement of fluid into and out of the cell struggled with a difficult biophysical question: how does water pass through the cell? Movement of water across the membrane was indicated almost as soon as the lipid bilayer was recognized as being the plasma membrane of cells, back in the 1920s. Simple diffusion of water across the lipid bilayer occurs through all biological membranes. However, its low velocity and finite extent soon became apparent, suggesting the existence of additional pathways for water moving through the membrane. In spite of the enormous amount of work carried out in this area, the precise and complete answer only came relatively recently with the discovery of aquaporins, transmembrane channel proteins making the membrane tenfold to 100-fold more permeable to water than membranes lacking such pores. The water conductance featured by the aquaporins is astonishing: in fact, each single aquaporin pore can conduct billions of water molecules per second. A branch of the aquaporin family, the aquaglyceroporins, features conductance to small neutral solutes in addition to water. This review summarizes recent updates on the molecular structure, regulation, biophysics, and biological functions of aquaporins. Possible biotechnological applications of aquaporins are also described.

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.

Differential Proteomic Shotgun Analysis Elucidates Involvement of Water Channel Aquaporin 8 in Presence of α-Amylase in the Colon

Aquaporin (AQP) family plays a pivotal role in fluid secretion and absorption, especially in the digestive system and secretory glands. Within this family, AQP8 was reported to be widely expressed in the epithelia of the digestive tract, liver, and pancreas. In two parallel experimental platforms with different analytical and comparative approaches, in-gel tryptic digestion with macro-embedded spreadsheet analysis and in-solution tryptic digestion with LC-MS alignment based approach, we compared wild-type and AQP8 knockout mice colon proteomes. Shared result between both experiments revealed down-regulation of α-amylase 2 in AQP8-deleted mice model. Verification on both transcriptional and translational levels confirmed the involvement of AQP8 in α-amylase 2 regulation. Given the profound role of AQP8 as a water and solutes transporter, it might be important in modulating α-amylase 2 synthesis by colonic epithelial cells as well. Here, we also proved the capability of our coupled approaches for selecting the most reliable and significant candidates, an applicable process for initial screening of biological biomarkers in complex specimens and tissue extracts.

In planta changes in protein phosphorylation induced by the plant hormone abscisic acid

Abscisic acid (ABA) is a hormone that controls seed dormancy and germination as well as the overall plant response to important environmental stresses such as drought. Recent studies have demonstrated that the ABA-bound receptor binds to and inhibits a class of protein phosphatases. To identify more broadly the phosphoproteins affected by this hormone in vivo, we used (14)N/(15)N metabolic labeling to perform a quantitative untargeted mass spectrometric analysis of the Arabidopsis thaliana phosphoproteome following ABA treatment. We found that 50 different phosphopeptides had their phosphorylation state significantly altered by ABA over a treatment period lasting 5-30 min. Among these changes were increases in phosphorylation of subfamily 2 SNF1-related kinases and ABA-responsive basic leucine zipper transcription factors implicated in ABA signaling by previous in vitro studies. Furthermore, four members of the aquaporin family showed decreased phosphorylation at a carboxy-terminal serine which is predicted to cause closure of the water-transporting aquaporin gate, consistent with ABA's role in ameliorating the effect of drought. Finally, more than 20 proteins not previously known to be involved with ABA were found to have significantly altered phosphorylation levels. Many of these changes are phosphorylation decreases, indicating that an expanded model of ABA signaling, beyond simple phosphatase inhibition, may be necessary. This quantitative proteomics dataset provides a more comprehensive, albeit incomplete, view both of the protein targets whose biochemical activities are likely to be controlled by ABA and of the nature of the emerging phosphorylation and dephosphorylation cascades triggered by this hormone.

Comparison of two dimensional electrophoresis mouse colon proteomes before and after knocking out Aquaporin 8

Aquaporin (AQP) family plays a fundamental role in transmembrane water and small solutes movement. Within this family, aquaporin 8 (AQP8), showed to be widely distributed in the digestive system especially colon. To investigate the possible protein alterations involved in AQP8 regulation and trafficking, we extensively compared between wild type and AQP8 knockout mouse colon using semi-quantitative fluorescence- stained two dimensional gel electrophoresis (2-DE) coupled with nano LC-Ms/Ms. Our analysis revealed identification and regulation of 21 proteins, most notably, actin-related family which suggests its possible involvement in regulating AQP8 secretory vesicles migration to be integrated as a cell membrane protein.

Aquaporins in the wild: natural genetic diversity and selective pressure in the PIP gene family in five Neotropical tree species.

BackgroundTropical trees undergo severe stress through seasonal drought and flooding, and the ability of these species to respond may be a major factor in their survival in tropical ecosystems, particularly in relation to global climate change. Aquaporins are involved in the regulation of water flow and have been shown to be involved in drought response; they may therefore play a major adaptive role in these species. We describe genetic diversity in the PIP sub-family of the widespread gene family of Aquaporins in five Neotropical tree species covering four botanical families.ResultsPIP Aquaporin subfamily genes were isolated, and their DNA sequence polymorphisms characterised in natural populations. Sequence data were analysed with statistical tests of standard neutral equilibrium and demographic scenarios simulated to compare with the observed results. Chloroplast SSRs were also used to test demographic transitions. Most gene fragments are highly polymorphic and display signatures of balancing selection or bottlenecks; chloroplast SSR markers have significant statistics that do not conform to expectations for population bottlenecks. Although not incompatible with a purely demographic scenario, the combination of all tests tends to favour a selective interpretation of extant gene diversity.ConclusionsTropical tree PIP genes may generally undergo balancing selection, which may maintain high levels of genetic diversity at these loci. Genetic variation at PIP genes may represent a response to variable environmental conditions.

Molecular Diversity of Vasotocin‐Dependent Aquaporins Closely Associated with Water Adaptation Strategy in Anuran Amphibians

Anuran amphibians represent the first vertebrates that adapted to terrestrial environments, and are successfully distributed around the world, even to forests and arid deserts. Many adult anurans have specialised osmoregulatory organs, in addition to the kidney (i.e. the ventral pelvic skin to absorb water from the external environments and a urinary bladder that stores water and reabsorbs it in times of need). Aquaporin (AQP), a water channel protein, plays a fundamental role in these water absorption/reabsorption processes. The anuran AQP family consists of at least AQP0-AQP5, AQP7-AQP10 and two anuran-specific types, designated as AQPa1 and AQPa2. For the three osmoregulatory organs, AQP3 is constitutively located in the basolateral membrane of the tight-junctioned epithelial cells, allowing water transport between the cytoplasm of these cells and the neighbouring tissue fluid at all times. On the other hand, AQPs at the apical side of the tight epithelial cells are different among these organs, and are named kidney-type AQP2, ventral pelvic skin-type AQPa2 and urinary bladder-type AQPa2. All of them show translocation from the cytoplasmic pool to the apical plasma membrane in response to arginine vasotocin, thereby regulating water transport independently in each osmoregulatory organ. It was further revealed that, in terrestrial and arboreal anurans, the bladder-type AQPa2 is expressed in the pelvic skin, together with the pelvic skin-type AQPa2, potentially facilitating water absorption from the pelvic skin. By contrast, Xenopus has lost the ability to efficiently produce pelvic skin-type AQPa2 (AQP-x3) because Cys-273 of AQP-x3 and/or Cys-273-coding region of AQPx3 mRNA attenuate gene expression at a post-transcriptional step, presumably leading to the prevention of excessive water influx in this aquatic species. Collectively, the acquisition of two forms of AQPa2 and the diversified regulation of their gene expression appears to provide the necessary mechanisms for the evolutionary adaptation of anurans to a wide variety of ecological environments.

Abstract 1752: Prognostic significance of Aquaporin(AQP) expression in gastric and colorectal cancer

Abstract Introduction : Aquaporins (AQPs) are a membrane proteins involved in water transport and have been found to be expressed in several cancers. We have already reported that AQP 5 expression is associated with differentiation for gastric cancer (J Physiol Science 2009). However, the role of AQP family expression has not been well evaluated yet. In this study, we examined the expression of AQP 1, 4, 5 and 8 in gastric cancer and colorectal cancer, and compared them with the clinico-pathological characteristics of the patients. Method : The expression of AQP1, 4, 5, and 8 was comprehensively examined by tissue microarray (TMA1150) that has been established in our hospital. The specimens of gastric cancer and colorectal cancer were obtained from the patients who receive an operation between 1993 to 2004. Clinico-pathological data were obtained from the patients’ medical records. After careful examination of two independent pathologists, the results were scored according to the intensity and the distribution. Finally, AQP expressions were compared to the clinical pathologic finding of the patients. Result : In stomach cancer, positivity of AQP1, 4, 5, and 8 expressions were 40.7% (22/54), 43.2% (19/44), 97.6% (41/42) and 18.2% (8/44) respectively. AQP4 positive patients have a significant better prognosis than that of negative patients (p=0.004) and low expression of AQP4 tended to relate to poorly differentiated adenocarcinoma (p=0.07). However there was no significant difference between the prognosis, histological type, disease stage (TNM classification) and AQP1, 5, and 8 expressions. With regard to colorectal cancer, positivity of AQP1, 4, 5, and 8 expressions were 27.4% (20/73), 45.9% (34/74), 98.4% (61/62), and 76.4% (55/72) respectively. AQP4 positive patients tended to have a favorable prognosis (p=0.12), on the other hand AQP1 positive group tended to have a worse prognosis (p=0.06). There was the other relationship between low expression of AQP4 and N factor (p=0.04). Conclusion : AQP 1 and 4 expression have some roles in the progression of gastric cancer and colorectal cancer, however the role of AQP 5 and 8 are still unknown. Our findings suggested that AQP 1 and 4 may be a molecular target of gastric cancer and colorectal cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1752.

The Gating Mechanism of Yeast Aquaporin Studied by Molecular Dynamics Simulations

Aquaporins are membrane proteins responsible for the permeation of water and other solutes through the cell membrane. They arrange in a tetrameric conformation, where each monomer acts as a highly efficient single-file water channel. The x-ray structure of the yeast aquaporin (Aqy1), recently found at a very high resolution (1.15 Angstrom), revealed the conformation of the extended N-terminus - an unusual feature within the family of aquaporins - occluding the water pore. In contrast, functional assays with spheroplast of P.

Determinant of Cation Blocking Behavior in Aquaporin-1

The most extensively studied member of the aquaporin family, wildtype (WT) aquaporin-1 (AQP1), has been shown to effectively block cations from permeation across the cell membrane, thus maintaining the osmotic pressure of the cell. Recent experiments have suggested the essential role that the Selectivity Filter (SF) region of the channel plays in blocking cation flux. In the present study, the potential of mean forces for permeation of sodium cation (Na+), potassium cation (K+), and classical hydronium cation (H3O+) (without the possibility of Grotthuss proton shuttling) are characterized for a series of AQP1 mutants. The free energy barriers for conducting hydrated excess protons (H+), which diffuse via the Grotthuss mechanism, are characterized as well, by utilizing the multi-state empirical valence bond (MS-EVB) method. The maximum cation conductance is calculated using the Poisson-Nerst-Planck theory. The present study reveals the key role of the SF domain in cation gating and provides insight into the subtle mechanism of proton permeation mutants of the AQP1 channel.