MIR phasing using merohedrally twinned crystals

Scheltinga, Anke C. Terwisscha van; Valegård, K.; Hajdu, János; Andersson, Ingemar

doi:10.1107/s090744490302122x

Cited by 10 publications

(10 citation statements)

References 20 publications

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“…This crystal form lacked the fourfold symmetry typically associated with AQP crystals (8,12), notable exceptions being one structure of AQPZ at 3.2-Å resolution (14) and the open conformation of SoPIP2;1 at 3.9-Å resolution (12). Crystals of AQP5 diffracted to 2.0-Å resolution (Table 1) but suffered from nearly perfect pseudomerohedral twinning (30). The structure was solved by molecular replacement with the use of a homology model (SI Text) derived from the bovine AQP1 structure (8).…”

Section: Resultsmentioning

confidence: 97%

High-resolution x-ray structure of human aquaporin 5

Horsefield

Nordén²,

Fellert³

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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Human aquaporin 5 (HsAQP5) facilitates the transport of water across plasma membranes and has been identified within cells of the stomach, duodenum, pancreas, airways, lungs, salivary glands, sweat glands, eyes, lacrimal glands, and the inner ear. AQP5, like AQP2, is subject to posttranslational regulation by phosphorylation, at which point it is trafficked between intracellular storage compartments and the plasma membrane. Details concerning the molecular mechanism of membrane trafficking are unknown. Here we report the x-ray structure of HsAQP5 to 2.0-Å resolution and highlight structural similarities and differences relative to other eukaryotic aquaporins. A lipid occludes the putative central pore, preventing the passage of gas or ions through the center of the tetramer. Multiple consensus phosphorylation sites are observed in the structure and their potential regulatory role is discussed. We postulate that a change in the conformation of the C terminus may arise from the phosphorylation of AQP5 and thereby signal trafficking.membrane protein ͉ trafficking ͉ crystallography ͉ water channel protein ͉ heterologous overexpression A quaporins (1) facilitate the flow of water across cellular membranes while preserving ion concentration gradients. By maintaining water homeostasis within cells, aquaporin family members play essential physiological roles within all kingdoms of life. They form a large superfamily containing both pure water channels, and channels also permeable to other small polar molecules such as glycerol (2). Thirteen human aquaporin (AQP) isoforms have been identified, and they govern a broad spectrum of physiological functions (2, 3). Examples include concentration of urine in the kidneys, release of tears and maintenance of lens transparency in the eye, maintenance of water homeostasis within the brain, the extrusion of sweat from the skin, control of glycerol concentration in fat metabolism, and facilitation of cell migration during angiogenesis.X-ray and electron diffraction studies have yielded crystal structures of mammalian AQP0 (4-6), AQP1 (7, 8), AQP2 (9), and AQP4 (10), plant SoPIP2;1 (11, 12), bacterial AQPZ (13,14), and GlpF (15), and the archaeal AQPM (16). These structures establish that phylogenetically and functionally diverse AQPs arrange as homotetramers, each protomer containing six highly conserved transmembrane (TM) ␣-helices. Two half-helices form a pseudoseventh TM helix because of the insertion of loops B and E into the membrane from opposite sides, placing both copies of the highly conserved Asn-Pro-Ala (NPA) AQP signature motif near the center of the water channel. The conserved aromatic/arginine (ar/R) constriction region imposes substrate selectivity on the channel (17). A consensus has emerged from molecular dynamics simulations regarding the mechanism of water transport and ion exclusion (18) establishing that an electrostatic potential barrier peaking at the NPA region prevents the cotranslocation of protons through the channel.Although the tissue-specific expressio...

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Section: Resultsmentioning

confidence: 97%

High-resolution x-ray structure of human aquaporin 5

Horsefield

Nordén²,

Fellert³

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

206

180

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“…The data was detwinned using DETWIN from the CCP4 suite 34 .Extensive molecular replacement was attempted essentially as described 35 but was unsuccessful in solving the phase problem. Initial heavy-atom positions of two platinum sites were found by SIRAS in SHELXC/D 36 using detwinned datasets where the estimated twin-fraction was matched between datasets and minimized as much as possible 37 . A single Ta 6 Br 12 -cluster site were identified using the initial platinum phases, and experimental MIRAS phases combining two platinum sites and one Ta 6 Br 12 -cluster site were calculated to 3.5 Å in SHARP 38 using detwinned datasets (Supplementary Fig.…”

Section: Methodsmentioning

confidence: 99%

Crystal structure of a eukaryotic phosphate transporter

Pedersen

Johri

Waight

et al. 2013

Nature

209

207

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“…It took many years to work out protocols for obtaining crystal structures for DAOCS in complex with its penicillin substrates and cephalosporin products. 4 The structural studies included de-twinning of each data set, 3,4,17,18 a procedure that amplifies errors. Despite persistent trials no other crystal form has been obtained so far.…”

Section: Introductionmentioning

confidence: 99%

“…These crystals diffracted X-rays to better than 1.3 Å resolution. Merohedral twinning is a packing anomaly [17][18][19] that in the past has prevented many a structure determination. In the twinned crystals, a trimer is formed by the interpenetration of the C-terminal arm (residues 308-311) of one monomer into the active site of the neighbouring molecule in a cyclic fashion.…”

Section: Introductionmentioning

confidence: 99%