Water Permeability of C-Terminally Truncated Aquaporin 0 (AQP0 1-243) Observed in the Aging Human Lens

Ball, Lauren E.; Little, Mark W.; Nowak, Mark W.; Garland, Donita; Crouch, Rosalie K.; Schey, Kevin L.

doi:10.1167/iovs.02-1317

Cited by 61 publications

(65 citation statements)

References 66 publications

(58 reference statements)

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“…These conductance characteristics are not changed by proteolytic cleavage of AQP0 24 . As our structure, obtained with the double-layered 2D crystals grown at pH 6 7 , reveals fewer water molecules in the pore than the structure determined from the 3D crystals grown at pH 10.5 8 , pore closure appears to be a result of junction formation, not pH shift.…”

Section: Water Molecules In the Aqp0 Porementioning

confidence: 86%

Lipid–protein interactions in double-layered two-dimensional AQP0 crystals

Gonen

Cheng

Sliz

et al. 2005

Nature

617

644

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Lens-specific aquaporin-0 (AQP0) functions as a specific water pore and forms the thin junctions between fibre cells. We describe a 1.9 Å resolution structure of junctional AQP0, determined by electron crystallography of double-layered two-dimensional crystals. Comparison of junctional and non-junctional AQP0 structures shows that junction formation depends on a conformational switch in an extracellular loop, which may result from cleavage of the cytoplasmic N-and C-termini. In the centre of the water pathway, the closed pore in junctional AQP0 retains only three water molecules, which are too widely spaced to form hydrogen bonds with each other. Packing interactions between AQP0 tetramers in the crystalline array are mediated by lipid molecules, which assume preferred conformations. We could therefore build an atomic model for the lipid bilayer surrounding the AQP0 tetramers, and we describe lipid-protein interactions. KeywordsAquaporin-0; lens; MIP; two-dimensional crystal; lipid-protein interaction; electron crystallography Members of the aquaporin (AQP) family form membrane pores that are either highly selective for water (aquaporins) or also permeable to other small neutral solutes such as glycerol and urea (aquaglyceroporins) (reviewed in 1 ). Structural studies have revealed that all AQPs share the same basic architecture, which consists of two tandem repeats, each containing a bundle of three transmembrane α-helices and a hydrophobic loop with the highly conserved asparagine-proline-alanine (NPA) motif 2 -8 . The two NPA-containing loops B and E fold back into the membrane and form short α-helices (HB and HE) that line the water pore. The ar/R constriction site, so named because it is formed by an aromatic and an arginine residue, confers water selectivity to AQP pores, while the NPA motifs play an important role in the proton exclusion mechanism (reviewed in 9 ).Correspondence to: Thomas Walz.Correspondence and requests for materials should be addressed to T.W. (twalz@hms.harvard.edu). Coordinates and structure factors for junctional and non-junctional AQP0 have been deposited in the Protein Data Bank (accession codes 2B6O and 2B6P, respectively).. Suplementary Information accompanies the paper on www.nature.com/nature. Competing interests statementThe authors declare that they have no competing financial interests. AQP0 is the most abundant protein in lens fibre cell membranes, where it forms not only water pores but also the 11-13 nm "thin lens junctions" that assemble upon proteolytic cleavage of the cytoplasmic termini 10 , 11 . We recently presented the structure of the AQP0-mediated membrane junction at 3 Å resolution as determined by electron crystallography of doublelayered two-dimensional (2D) crystals 7 . The structure showed that AQP0 junctions are stabilised by specific interactions between tetramers in adjoining membranes involving almost exclusively proline residues. Calculated pore profiles also showed that the pore in junctional AQP0 is highly constricted due to a substantially ...

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Section: Water Molecules In the Aqp0 Porementioning

confidence: 86%

Lipid–protein interactions in double-layered two-dimensional AQP0 crystals

Gonen

Cheng

Sliz

et al. 2005

Nature

617

644

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“…13 Treatment of AQP0 with proteolytic enzymes generates more junctional AQP0 13 and structural characterization suggests the truncated junctional form has a closed water pore. 49 However, functional studies demonstrated equal permeability of full-length and truncated AQP0, 11,50 and showed full-length AQP0 has adhesive properties. 12 Another possible consequence of Cterminal truncation is that key residues involved in AQP0 protein-protein interactions are removed.…”

Section: Discussionmentioning

confidence: 99%

MALDI Imaging Mass Spectrometry Spatially Maps Age-Related Deamidation and Truncation of Human Lens Aquaporin-0

Wenke

Rose

Spraggins

et al. 2015

Invest. Ophthalmol. Vis. Sci.

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Citation: Wenke JL, Rose KL, Spraggins JM, Schey KL. MALDI imaging mass spectrometry spatially maps agerelated deamidation and truncation of human lens Aquaporin-0. Invest Ophthalmol Vis Sci. 2015;56:7398-7405. DOI:10.1167/iovs.15-18117 PURPOSE. To spatially map human lens Aquaporin-0 (AQP0) protein modifications, including lipidation, truncation, and deamidation, from birth through middle age using matrix-assisted laser desorption ionization (MALDI) imaging mass spectrometry (IMS). METHODS.Human lens sections were water-washed to facilitate detection of membrane protein AQP0. We acquired MALDI images from eight human lenses ranging in age from 2 months to 63 years. In situ tryptic digestion was used to generate peptides of AQP0 and peptide images were acquired on a 15T Fourier transform ion cyclotron resonance (FTICR) mass spectrometer. Peptide extracts were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and database searched to identify peptides observed in MALDI imaging experiments.RESULTS. Unmodified, truncated, and fatty acid-acylated forms of AQP0 were detected in protein imaging experiments. Full-length AQP0 was fatty acid acylated in the core and cortex of young (2-and 4-month) lenses. Acylated and unmodified AQP0 were C-terminally truncated in older lens cores. Deamidated tryptic peptides (þ0.9847 Da) were mass resolved from unmodified peptides by FTICR MS. Peptide images revealed differential localization of un-, singly-, and doubly-deamidated AQP0 C-terminal peptide (239-263). Deamidation was present at 4 months and increases with age. Liquid chromatography-MS/MS results indicated N246 undergoes deamidation more rapidly than N259. CONCLUSIONS.Results indicated AQP0 fatty acid acylation and deamidation occur during early development. Progressive age-related AQP0 processing, including deamidation and truncation, was mapped in human lenses as a function of age. The localization of these modified AQP0 forms suggests where AQP0 functions may change throughout lens development and aging.

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“…The discovery of AQP1 as a water channel in RBCs by Peter Agre's lab (Preston et al, 1994) suggested the closely related AQP0 might also be a water channel. Subsequent in vitro expression of AQP0 in Xenopus oocytes showed that AQP0 does function as a water channel (Kushmerick et al, 1995;Mulders et al, 1995;Chandy et al, 1997;Francis et al, 2000a,b;Schey et al, 2000;Chepelinsky, 2003;Ball et al, 2003) and possibly also as a glycerol transporter (Kushmerick et al, 1998). Varadaraj et al (1999Varadaraj et al ( , 2005 investigated the function of AQP0 in the mammalian lens and corroborated its role as a water transporter but found no evidence for glycerol transport.…”

Section: Introductionmentioning

confidence: 99%

Functional expression of aquaporins in embryonic, postnatal, and adult mouse lenses

Varadaraj

Kumari

Mathias

2007

Developmental Dynamics

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Aquaporin 0 (AQP0) and AQP1 are expressed in the lens, each in a different cell type, and their functional roles are not thoroughly understood. Our previous study showed that these two AQPs function as water transporters. In order to further understand the functional significance of these two different aquaporins in the lens, we investigated their initiation and continued expression. AQP0 transcript and protein were first detected at embryonic stage (E) 11.25 in the differentiating primary fiber cells of the developing lens; its synthesis continued through the adult stage in the secondary fiber cells. Low levels of AQP1 expression were first seen in lens anterior epithelial cells at E17.5; following postnatal day (P) 6.5, the expression gradually progressed towards the equatorial epithelial cells. In the postnatal lens, the increase in membrane water permeability of epithelial cells and lens transparency coincides with the increase in AQP1 expression. AQP1 expression reaches its peak at P30 and continues through the adult stage both in the anterior and equatorial epithelial cells. The enhancement in AQP1 expression concomitant with the increase in the size of the lens suggests the progression in the establishment of the lens microcirculatory system. In vitro and in vivo studies show that both aquaporins share at least one important function, which is water transport in the lens microcirculatory system. However, the temporal expression of these two AQPs suggests an apparently unique role/s in lens development and transparency. To our knowledge, this is the first report on the expression patterns of AQP0 and AQP1 during lens development and differentiation and their relation to lens transparency. Developmental Dynamics 236:1319 -1328, 2007.

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Water Permeability of C-Terminally Truncated Aquaporin 0 (AQP0 1-243) Observed in the Aging Human Lens

Abstract: These data provide evidence that loss of 20 amino acids from the C terminus may not directly affect the ability of AQP0 to transport water.

Cited by 61 publications

References 66 publications

Lipid–protein interactions in double-layered two-dimensional AQP0 crystals

Lipid–protein interactions in double-layered two-dimensional AQP0 crystals

MALDI Imaging Mass Spectrometry Spatially Maps Age-Related Deamidation and Truncation of Human Lens Aquaporin-0

Functional expression of aquaporins in embryonic, postnatal, and adult mouse lenses

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