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Foguesatto K, Bastos CLQ, Boyle RT, Nery LEM, Souza MM. Participation of Na+/K+-ATPase and aquaporins in the uptake of water during moult processes in the shrimp Palaemon argentinus (Nobili, 1901). J Comp Physiol B 2019; 189:523-535. [DOI: 10.1007/s00360-019-01232-w] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2019] [Revised: 08/08/2019] [Accepted: 08/21/2019] [Indexed: 11/28/2022]
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3
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Emami S, Fan Y, Munro R, Ladizhansky V, Brown LS. Yeast-expressed human membrane protein aquaporin-1 yields excellent resolution of solid-state MAS NMR spectra. JOURNAL OF BIOMOLECULAR NMR 2013; 55:147-155. [PMID: 23344971 DOI: 10.1007/s10858-013-9710-5] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2012] [Accepted: 01/15/2013] [Indexed: 06/01/2023]
Abstract
One of the biggest challenges in solid-state NMR studies of membrane proteins is to obtain a homogeneous natively folded sample giving high spectral resolution sufficient for structural studies. Eukaryotic membrane proteins are especially difficult and expensive targets in this respect. Methylotrophic yeast Pichia pastoris is a reliable producer of eukaryotic membrane proteins for crystallography and a promising economical source of isotopically labeled proteins for NMR. We show that eukaryotic membrane protein human aquaporin 1 can be doubly ((13)C/(15)N) isotopically labeled in this system and functionally reconstituted into phospholipids, giving excellent resolution of solid-state magic angle spinning NMR spectra.
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Affiliation(s)
- Sanaz Emami
- Departments of Physics, and Biophysics Interdepartmental Group, University of Guelph, 50 Stone Road East, Guelph, ON, N1G 2W1, Canada
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4
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Al-Mbaideen A, Benaissa M. Frequency self deconvolution in the quantitative analysis of near infrared spectra. Anal Chim Acta 2011; 705:135-47. [DOI: 10.1016/j.aca.2011.04.037] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2010] [Revised: 04/03/2011] [Accepted: 04/18/2011] [Indexed: 10/18/2022]
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5
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Abstract
Arginine vasopressin (AVP), also known as vasopressin or anti-diuretic hormone, is a neuropeptide produced in the hypothalamus. It is primarily responsible for osmoregulation and thus maintains body fluid homeostasis. It is also a potent vasoconstrictor, may have a role in higher cognitive functions and affects metabolism. All the biological and cellular effects of vasopressin are mediated by the interaction of this hormone with three G-protein-coupled receptors - V(1a), V(1b) and V(2).Urological applications are based on the rationale that V(2) receptors mediate water conservation and increase urine osmolality. Due to their anti-diuretic properties mediated by the V(2) receptors, synthetic vasopressin agonists, such as desmopressin, are now commonly used for the treatment of nocturnal polyuria, central diabetes insipidus and nocturnal enuresis and potentially in urinary incontinence. Desmopressin has been licenced worldwide for haematological indications of haemophilia and von Willebrand disease. Vasopressin receptor antagonists correct hyponatremia by blocking the activation of the V(2) receptor and induce a free water diuresis without an accompanying natriuresis or kaliuresis; an effect termed 'aquaresis'. Interfering with vasopressin signalling by administering vasopressin antagonists may have clinical benefits in acute and chronic heart failure.
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6
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Abstract
Water is the most abundant molecule in any cell. Specialized membrane channel, proteins called aquaporins, facilitate water transport across cell membranes. At least seven aquaporins (AQP): 1, 2, 3, 4, 6, 7, and 11 are expressed in the kidneys. Aquaporins play a role in both the short-term and long-term regulation of water balance as well as in the pathophysiology of water balance disorders. Aquaporin is composed of a single peptide chain consisting of approximately 270 amino acids. Inherited central and nephrogenic diabetes insipidus are primarily due to the decreased expression of AQP2 while mutation in the AQP2 molecule is responsible for inherited central diabetes insipidus. In acquired causes of nephrogenic diabetes insipidus, there is a downregulation of AQP2 expression in the inner medulla of the kidney. Nephrotic syndrome is characterized by excessive sodium and water reabsorption, although in spite of this, patients do not develop hyponatremia. There is a marked downregulation of both AQP2 and AQP3 expression, which could be a physiologic response to extracellular water reabsorption in patients with nephrotic syndrome. There are some conditions in which aquaporin expression has been found to increase such as experimentally induced heart failure, cirrhosis, and pregnancy. Some drugs such as cisplatin and cyclosporine, also alter the expression of aquaporins. The three-pore model of peritoneal transport depicts the importance of aquaporins. Thus, the understanding of renal water channels has solved the mystery behind many water balance disorders. Further insights into the molecular structure and biology of aquaporins will help to lay a foundation for the development of future drugs.
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Affiliation(s)
- S K Agarwal
- Department of Nephrology, All India Institute of Medical Sciences, New Delhi - 110 029, India
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Kwaambwa H, Maikokera R. Infrared and circular dichroism spectroscopic characterisation of secondary structure components of a water treatment coagulant protein extracted from Moringa oleifera seeds. Colloids Surf B Biointerfaces 2008; 64:118-25. [DOI: 10.1016/j.colsurfb.2008.01.014] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2007] [Revised: 01/11/2008] [Accepted: 01/11/2008] [Indexed: 10/22/2022]
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8
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Turk E, Gasymov OK, Lanza S, Horwitz J, Wright EM. A reinvestigation of the secondary structure of functionally active vSGLT, the vibrio sodium/galactose cotransporter. Biochemistry 2006; 45:1470-9. [PMID: 16445289 DOI: 10.1021/bi052160z] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The bacterial Na(+)/galactose cotransporter vSGLT of Vibrio parahaemolyticus is a member of the sodium:solute symporter family (SSS). Previous studies using electron microscopy have shown that vSGLT is a monomeric protein. Computational and experimental topological analyses have consistently indicated that this protein possesses 14 transmembrane alpha-helices. Our previous study using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) to quantitate secondary structure content had indicated, in contrast, an alpha-helical content of only 35%, too little to be consistent with the 14-span model [le Coutre, J., et al. (2002) Biochemistry 41, 8082-6]. ATR-FTIR had also indicated that upon binding of Na(+) and d-galactose, the alpha-helical content increased to 53%. Here we revisit the vSGLT secondary structural distribution using an alternative approach, ultraviolet circular dichroism spectropolarimetry (CD), which is highly accurate in determining the alpha-helical content of a protein in solution. CD spectra were obtained from actively functional, soluble vSGLT and, as an internal check, from a fusion protein of vSGLT and the beta-barrel green fluorescent protein (GFP). Far-UV CD of vSGLT indicates a predominating 85% alpha-helical content, and an absence of beta-strands. Far-UV CD of the vSGLT-GFP fusion corroborates this profile, indicating an equivalent alpha-helical content, and a beta-strand content consistent with the GFP contribution. No detectable substrate-induced macroscopic changes in secondary structure are apparent in the far UV. In the near UV, increases in positive CD intensity occur in a stepwise manner with added substrates, implying changing environments of aromatic amino acid residues. CD thus confirms the current 14-transmembrane span model of vSGLT and reveals distinct substrate-induced conformational changes. The high percentage of alpha-helical structure found requires, when considered in the context of membrane topology, that nearly a third of the total alpha-helical fraction lies in extramembrane domains, which distinguishes this cotransporter from the unrelated lactose and glycerol 3-phosphate transporters.
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Affiliation(s)
- Eric Turk
- Department of Physiology, David Geffen School of Medicine at UCLA, University of California, 90095-1751, USA.
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9
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Abstract
Endocrine pancreatic tumours (EPTs) are uncommon tumours occurring in approximately 1 in 100,000 of the population, representing 1-2% of all pancreatic neoplasms. Some of the tumours may be part of multiple endocrine neoplasia type one (MEN-1) syndrome or von Hippel-Lindau (vHL) disease. EPTs are classified as functioning or non-functioning tumours on the basis of their clinical manifestation. The biochemical diagnosis of EPT is based on hormones and amines released. Besides specific markers such as insulin, there are also general tumour markers such as chromogranin A, which is the most valuable marker and has been reported to be increased in plasma in 50-80% of patients with EPTs and correlates with tumour burden. The location of endocrine tumours of the pancreas includes different techniques, from endoscopic investigations to scintigraphy (e.g. somatostatin receptor scintigraphy) and positron emission tomography. The medical treatment of endocrine pancreatic tumours consists of chemotherapy, somatostatin analogues and alpha-interferon. None of these can cure a patient with malignant disease. In future, therapy will be custom-made and based on current knowledge of tumour biology and molecular genetics.
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Affiliation(s)
- Kjell Oberg
- Department of Medical Sciences, University Hospital, 751 85 Uppsala, Sweden.
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Vidossich P, Cascella M, Carloni P. Dynamics and energetics of water permeation through the aquaporin channel. Proteins 2004; 55:924-31. [PMID: 15146490 DOI: 10.1002/prot.10642] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Structural properties of water inside bovine aquaporin-1 are investigated by molecular simulation. The calculations, which are based on the recently determined X-ray structure at 2.2 A resolution (Sui et al., Nature 2001;414:872-878), are carried out on one monomeric subunit immersed in a water-n-octane-water bilayer. Molecular dynamics (MD) simulations suggest that His182, a fully conserved residue in the channel pore, is protonated in the delta position. Furthermore, they reveal a highly ordered water structure in the channel, induced by the electrostatic properties of the protein. Multiple-steering MD simulations are used to calculate the free-energy of water diffusion. To the best of our knowledge, this represents the first free-energy calculation based on the new, high-resolution structure of the pore. The calculated barrier is 2.5 kcal/mol, and it is associated to water permeation through the Asn-Pro-Ala (NPA) region of the pore, where water molecules are only hydrogen-bonded with themselves. These findings are fully consistent with those based on the previous MD studies on the human protein (de Groot and Grubmüller, Science 2001;294:2353-2357).
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Affiliation(s)
- Pietro Vidossich
- International School for Advanced Studies, S.I.S.S.A. and INFM-Democritos Modeling Center for Research In Atomistic Simulation, Trieste, Italy
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Oberg KA, Ruysschaert JM, Goormaghtigh E. The optimization of protein secondary structure determination with infrared and circular dichroism spectra. ACTA ACUST UNITED AC 2004; 271:2937-48. [PMID: 15233789 DOI: 10.1111/j.1432-1033.2004.04220.x] [Citation(s) in RCA: 145] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
We have used the circular dichroism and infrared spectra of a specially designed 50 protein database [Oberg, K.A., Ruysschaert, J.M. & Goormaghtigh, E. (2003) Protein Sci. 12, 2015-2031] in order to optimize the accuracy of spectroscopic protein secondary structure determination using multivariate statistical analysis methods. The results demonstrate that when the proteins are carefully selected for the diversity in their structure, no smaller subset of the database contains the necessary information to describe the entire set. One conclusion of the paper is therefore that large protein databases, observing stringent selection criteria, are necessary for the prediction of unknown proteins. A second important conclusion is that only the comparison of analyses run on circular dichroism and infrared spectra independently is able to identify failed solutions in the absence of known structure. Interestingly, it was also found in the course of this study that the amide II band has high information content and could be used alone for secondary structure prediction in place of amide I.
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Affiliation(s)
- Keith A Oberg
- Center for Structural Biology and Bioinformatics, Laboratory for the Structure and Function of Biological Membranes, Free University of Brussels (ULB), Belgium
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Rigler P, Ulrich WP, Hovius R, Ilegems E, Pick H, Vogel H. Downscaling Fourier Transform Infrared Spectroscopy to the Micrometer and Nanogram Scale: Secondary Structure of Serotonin and Acetylcholine Receptors. Biochemistry 2003; 42:14017-22. [PMID: 14636070 DOI: 10.1021/bi035113k] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
High signal-to-noise Fourier transform infrared (FTIR) spectra of the 5-hydroxytryptamine (serotonin) receptor (5-HT(3)R) and the nicotinic acetylcholine receptor (nAChR) were obtained by microscope FTIR spectroscopy using micrometer-sized, fully hydrated protein films. Because this novel procedure requires only nanogram quantities of membrane proteins, which is 4-5 orders of magnitude less than the amount of protein typically used for conventional FTIR spectroscopy, it opens the possibility to access the structure and dynamics of many important mammalian receptor proteins. The secondary structure of detergent-solubilized 5-HT(3)R determined by curve fitting of the amide I band yielded 36% alpha-helix, 33% beta-strand, 15% beta-turn, and 16% nonregular structures, which remained unchanged upon reconstitution in lipid membranes. From hydrogen-deuterium exchange, the secondary structure of the water-accessible part of 5-HT(3)R was determined as 14% alpha-helix, 16% beta-strand, 26% beta-turn, and 14% nonregular structures. Interestingly, we found that both the overall and the water-accessible nAChR secondary structures were nearly identical to those of 5-HT(3)R, in agreement with predicted structures of this class of receptors. This is the first time that structural investigations were obtained for two closely related ligand-gated ion channels under strictly identical experimental conditions.
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Affiliation(s)
- Per Rigler
- Laboratoire de Chimie Physique des Polymères et Membranes, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Ecublens, Switzerland
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Vass E, Hollósi M, Besson F, Buchet R. Vibrational spectroscopic detection of beta- and gamma-turns in synthetic and natural peptides and proteins. Chem Rev 2003; 103:1917-54. [PMID: 12744696 DOI: 10.1021/cr000100n] [Citation(s) in RCA: 246] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Elemér Vass
- Department of Organic Chemistry, Eötvös Loránd University, H-1518 Budapest 112, P.O. Box 32, Hungary
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Morrow JA, Hatters DM, Lu B, Hochtl P, Oberg KA, Rupp B, Weisgraber KH. Apolipoprotein E4 forms a molten globule. A potential basis for its association with disease. J Biol Chem 2002; 277:50380-5. [PMID: 12393895 DOI: 10.1074/jbc.m204898200] [Citation(s) in RCA: 159] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The amino-terminal domain of apolipoprotein (apo) E4 is less susceptible to chemical and thermal denaturation than the apoE3 and apoE2 domains. We compared the urea denaturation curves of the 22-kDa amino-terminal domains of the apoE isoforms at pH 7.4 and 4.0. At pH 7.4, apoE3 and apoE4 reflected an apparent two-state denaturation. The midpoints of denaturation were 5.2 and 4.3 m urea, respectively. At pH 4.0, a pH value known to stabilize folding intermediates, apoE4 and apoE3 displayed the same order of denaturation but with distinct plateaus, suggesting the presence of a stable folding intermediate. In contrast, apoE2 proved the most stable and lacked the distinct plateau observed with the other two isoforms and could be fitted to a two-state unfolding model. Analysis of the curves with a three-state unfolding model (native, intermediate, and unfolded) showed that the apoE4 folding intermediate reached its maximal concentration ( approximately 90% of the mixture) at 3.75 m, whereas the apoE3 intermediate was maximal at 4.75 m ( approximately 80%). These results are consistent with apoE4 being more susceptible to unfolding than apoE3 and apoE2 and more prone to form a stable folding intermediate. The structure of the apoE4 folding intermediate at pH 4.0 in 3.75 m urea was characterized using pepsin proteolysis, Fourier transform infrared spectroscopy, and dynamic light scattering. From these studies, we conclude that the apoE4 folding intermediate is a single molecule with the characteristics of a molten globule. We propose a model of the apoE4 molten globule in which the four-helix bundle of the amino-terminal domain is partially opened, generating a slightly elongated structure and exposing the hydrophobic core. Since molten globules have been implicated in both normal and abnormal physiological function, the differential abilities of the apoE isoforms to form a molten globule may contribute to the isoform-specific effects of apoE in disease.
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Affiliation(s)
- Julie A Morrow
- Gladstone Institutes of Cardiovascular Disease and Neurological Disease, San Francisco, California 94141-9100, USA
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15
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Smith SO, Eilers M, Song D, Crocker E, Ying W, Groesbeek M, Metz G, Ziliox M, Aimoto S. Implications of threonine hydrogen bonding in the glycophorin A transmembrane helix dimer. Biophys J 2002; 82:2476-86. [PMID: 11964235 PMCID: PMC1302037 DOI: 10.1016/s0006-3495(02)75590-2] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
The transmembrane helix of glycophorin A contains a seven-residue motif, LIxxGVxxGVxxT, that mediates protein dimerization. Threonine is the only polar amino acid in this motif with the potential to stabilize the dimer through hydrogen-bonding interactions. Polarized Fourier transform infrared spectroscopy is used to establish a robust protocol for incorporating glycophorin A transmembrane peptides into membrane bilayers. Analysis of the dichroic ratio of the 1655-cm(-1) amide I vibration indicates that peptides reconstituted by detergent dialysis have a transmembrane orientation with a helix crossing angle of <35 degrees. Solid-state nuclear magnetic resonance spectroscopy is used to establish high resolution structural restraints on the conformation and packing of Thr-87 in the dimer interface. Rotational resonance measurement of a 2.9-A distance between the gamma-methyl and backbone carbonyl carbons of Thr-87 is consistent with a gauche- conformation for the chi1 torsion angle. Rotational-echo double-resonance measurements demonstrate close packing (4.0 +/- 0.2 A) of the Thr-87 gamma-methyl group with the backbone nitrogen of Ile-88 across the dimer interface. The short interhelical distance places the beta-hydroxyl of Thr-87 within hydrogen-bonding range of the backbone carbonyl of Val-84 on the opposing helix. These results refine the structure of the glycophorin A dimer in membrane bilayers and highlight the complementary role of small and polar residues in the tight association of transmembrane helices in membrane proteins.
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Affiliation(s)
- Steven O Smith
- Department of Biochemistry and Cell Biology, Center for Structural Biology, State University of New York at Stony Brook, Stony Brook, New York 11794-5115, USA.
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Vassilenko KS, Uversky VN. Native-like secondary structure of molten globules. BIOCHIMICA ET BIOPHYSICA ACTA 2002; 1594:168-77. [PMID: 11825619 DOI: 10.1016/s0167-4838(01)00303-x] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The most common evidence for the existence of secondary structure in a globular protein is the presence of a strongly pronounced far-UV circular dichroism (CD) spectrum. Although CD spectra of native proteins are well described and their quantitative analysis is widely used, similar studies for denatured proteins have still to be done. Far-UV CD spectra of nine proteins in the native and the pH-induced molten globule states were acquired and analyzed. Singular value decomposition showed that the spectra of molten globules could be described as a superposition of at least three independent components (most likely alpha-, beta- and irregular structure). A self-consistent procedure of CD spectra analysis revealed the existence of a clear correlation between the shape of the molten globule spectra and the content of secondary structure elements in the corresponding native proteins, as determined from X-ray data. A mathematical expression of this correlation in terms of the Pierson coefficient amounts to the value of 0.9 for both the alpha-helix and the beta-structure. Thus, the secondary structure of proteins in the molten globule state is close to that in the native state.
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Affiliation(s)
- Konstantin S Vassilenko
- Institute of Protein Research, Russian Academy of Sciences, 142290 Pushchino, Moscow Region, Russia
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Permyakov SE, Oberg KA, Cherskaya AM, Shavlovsky MM, Permyakov EA, Uversky VN. Human alpha-fetoprotein as a Zn(2+)-binding protein. Tight cation binding is not accompanied by global changes in protein structure and stability. BIOCHIMICA ET BIOPHYSICA ACTA 2002; 1586:1-10. [PMID: 11781144 DOI: 10.1016/s0925-4439(01)00079-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The binding of zinc to human alpha-fetoprotein (AFP) isolated from human umbilical cord serum was studied by fluorimetric Zn(2+)-titration. We found that the total number of strong binding sites for zinc on this protein was 5: AFP has one very strong (dissociation constant, K(d)<10(-8) M) and at least four lower affinity zinc binding sites (K(d)<10(-5) M). Fourier transform infrared (FTIR) analysis revealed that aspartate and histidine residues could be involved in the strong coordination of zinc. Intriguingly, binding of zinc to the protein does not induce structural changes that can be detected by circular dichroism, FTIR, intrinsic fluorescence or (1,1')-bi-(4-anilino)naphthalene-5,5'-disulfonic acid (bis-ANS) binding. Finally, scanning microcalorimetry measurements showed that stability of the protein is also unaffected by zinc binding in spite of the strength of the coordination. Such strong interactions without major structural consequences are highly unusual, and AFP may therefore be the first characterized representative of a new class of ligand-binding proteins.
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Affiliation(s)
- Serge E Permyakov
- Institute for Biological Instrumentation, Russian Academy of Sciences, Pushchino, Moscow Region, Russia
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18
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Kosarikov DN, Lee JM, Uversky VN, Counts Gerber N. Role of conformational changes in the heme-dependent regulation of human soluble guanylate cyclase. J Inorg Biochem 2001; 87:267-76. [PMID: 11744065 DOI: 10.1016/s0162-0134(01)00387-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Soluble guanylate cyclase (sGC) is a receptor for endogenous and exogenous nitric oxide (NO) and is activated many fold upon its binding, making it a core enzyme in the nitric oxide signal transduction pathway. Much effort has been made to understand the link between binding of NO at the sGC heme and activation of the cyclase activity. We report here the first direct evidence for the role of conformational changes in transmitting the signal between the heme and cyclase domains. Using both circular dichroism (CD) and fluorescence spectroscopies, we have probed the effect that the sGC activators NO and 3-(5'-hydroxymethyl-2'-furyl)-1-benzyl-indazole (YC-1) and the inhibitor 1H-[1,2,4]-oxadiazolo-[4,3-a]-quinoxalin-1-one (ODQ) have on the structure of the protein. Surprisingly, binding of either ODQ or YC-1 to NO-bound sGC cause virtually identical changes in the far-UV CD spectra of sGC, reflecting a perturbation in the secondary structure of the enzyme. This change is absent upon binding of NO, YC-1 or ODQ alone. Using this and previous data, we propose a working model for the mechanism of activation of sGC by NO and YC-1 and inhibition by ODQ.
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Affiliation(s)
- D N Kosarikov
- Department of Chemistry and Biochemistry, San Francisco State University, 1600 Holloway Avenue, San Francisco, CA 94132-4163, USA
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Lórenz VA, Villaverde J, Trézéguet V, Lauquin GJ, Brandolin G, Padrós E. The secondary structure of the inhibited mitochondrial ADP/ATP transporter from yeast analyzed by FTIR spectroscopy. Biochemistry 2001; 40:8821-33. [PMID: 11467943 DOI: 10.1021/bi010091s] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Fourier transform infrared spectroscopy has been applied to the study of the carboxyatractyloside-inhibited mitochondrial ADP/ATP transporter from the yeast Saccharomyces cerevisiae, either solubilized in dodecyl maltoside or reconstituted in phosphatidylcholine liposomes. Its secondary structure has been estimated by means of Fourier self-deconvolution followed by curve fit. A Voigt function was used to fit the components of the deconvoluted spectrum, aiming to account for any distortions introduced by deconvolution. For any of the states analyzed, reconstituted or solubilized, in solution or in dry films, 60-70% of the amino acids are found to adopt alpha-helix plus unordered structures, coherent with the six transmembrane spanning helix model. Moreover, the problem of structure preservation on drying was addressed, and several observations pointed to a maintenance of the protein structure in dry films. Comparison of reconstituted and solubilized samples indicated the presence of both lipid-induced changes in the protein (decrease of the beta-sheets and increase of unordered structures) and protein-induced changes in the lipids (strong hydrogen bonding of lipid C=O groups). To obtain a better discrimination of alpha-helix and unordered structure contributions for the reconstituted form, H/D exchange experiments were performed. Between 35% and 45% of the amino acids were finally assigned to alpha-helix structures, compatible with the existence of five or six transmembrane spanning helices in the transporter. The level of H/D exchange was determined after 15 h of exposure to D(2)O vapor to be 85%, reflecting a high accessibility of the amide hydrogens even for the carboxyatractyloside-inhibited state.
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Affiliation(s)
- V A Lórenz
- Unitat de Biofísica, Departament de Bioquímica i de Biologia Molecular, Facultat de Medicina, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain
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Mitra AK. Three-Dimensional Organization of the aquaporin water channel: what can structure tell us about function? VITAMINS AND HORMONES 2001; 62:133-66. [PMID: 11345897 DOI: 10.1016/s0083-6729(01)62003-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/20/2023]
Affiliation(s)
- A K Mitra
- Department of Cell Biology, Scripps Research Institute, La Jolla, California 92037, USA
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21
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Acha V, Ruysschaert JM, Goormaghtigh E. Stacks of close to 100 phospholipid bilayers fully accessible to proteins. Anal Chim Acta 2001. [DOI: 10.1016/s0003-2670(01)00873-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Kosarikov DN, Young P, Uversky VN, Gerber NC. Human Soluble Guanylate Cyclase: Functional Expression, Purification and Structural Characterization. Arch Biochem Biophys 2001; 388:185-97. [PMID: 11368154 DOI: 10.1006/abbi.2001.2284] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Soluble guanylate cyclase is an enzyme that catalyzes formation of cGMP from GTP and is a member of the nucleotide cyclase family of enzymes. sGC is a receptor for endogenous and exogenous nitric oxide and is activated several-fold upon its binding, constituting a core enzyme in the nitric oxide signal transduction pathway. cGMP generated by sGC is an important second messenger that regulates activity of several enzymes triggering such important physiologic reactions as vasodilation, smooth muscle relaxation and platelet aggregation. We report here the functional expression of the human isoform of soluble guanylate cyclase in HighFive insect cells using a baculovirus expression system. Highly active recombinant protein was obtained without heme reconstitution or supplementation of the cell growth medium and the level of protein expression was found to be heavily affected by the composition of the growth medium. We have successfully purified highly active sGC (sp act up to 940 nmol/min/mg) from adherent cultures using a three-column, 1-day procedure. The UV-Vis spectrum of the isolated protein shows a Soret band at 431 nm, consistent with a histidine-ligated, 5-coordinate heme as previously reported. Far UV CD spectroscopy, intrinsic tryptophan fluorescence, fluorescence of the hydrophobic dye bis-ANS, size-exclusion chromatography, and small angle X-ray scattering (SAXS) were used to characterize the structural properties of the purified sGC. We used two hierarchical neural network methods to predict the secondary structure of sGC and found it to be consistent with the observed CD spectrum of sGC.
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Affiliation(s)
- D N Kosarikov
- Department of Chemistry and Biochemistry, San Francisco State University, California, USA
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23
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Stahlberg H, Heymann B, Mitsuoka K, Fuyijoshi Y, Engel A. Chapter 2 The aquaporin superfamily: Structure and function. CURRENT TOPICS IN MEMBRANES 2001. [DOI: 10.1016/s1063-5823(01)51004-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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24
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Abrecht H, Goormaghtigh E, Ruysschaert JM, Homble F. Structure and orientation of two voltage-dependent anion-selective channel isoforms. An attenuated total reflection fourier-transform infrared spectroscopy study. J Biol Chem 2000; 275:40992-9. [PMID: 11018035 DOI: 10.1074/jbc.m006437200] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Two VDAC (voltage-dependent anion-selective channel) isoforms were purified from seed cotyledons of Phaseolus vulgaris by chromatofocusing chromatography. Attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy was used to study the structural properties of the two isoforms reconstituted in a mixture of asolectin and 5% stigmasterol. The IR spectra of the two VDAC isoforms were highly similar indicating 50 to 53% anti-parallel beta-sheet. The orientation of the beta-strands relative to the barrel axis was calculated from the experimentally obtained dichroic ratios of the amide I beta-sheet component and the amide II band. Comparing the IR spectra of the reconstituted VDAC isoforms with the IR spectra of the bacterial porin OmpF, for which a high resolution structure is available, provided evidence for a general structural organization of the VDAC isoforms similar to that of bacterial porins. Hydrogen-deuterium exchange measurements indicated that the exchange of the amide protons occurs to a higher extent in the two VDAC isoforms than in the OmpF porin.
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Affiliation(s)
- H Abrecht
- Laboratoire de Physiologie Végétale, CP 206/2, Faculté des Sciences, Université Libre de Bruxelles, Bld du Triomphe, B-1050 Brussels, Belgium
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25
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Harvengt P, Vlerick A, Fuks B, Wattiez R, Ruysschaert JM, Homble F. Lentil seed aquaporins form a hetero-oligomer which is phosphorylated by a Mg(2+)-dependent and Ca(2+)-regulated kinase. Biochem J 2000; 352 Pt 1:183-90. [PMID: 11062071 PMCID: PMC1221445] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/18/2023]
Abstract
In plants, aquaporins regulate the water flow through membranes during growth, development and stress responses. We have isolated two isoforms of the aquaporin family from the protein-storage vacuoles of lentil (Lens culinaris Med.) seeds. Chemical cross-linking experiments showed that both isoforms belong to the same oligomer in the membrane and are phosphorylated by a membrane-bound protein kinase. We assigned the kinase activity to a 52 kDa protein that is magnesium-dependent and calcium-regulated.
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Affiliation(s)
- P Harvengt
- Laboratoire de Physiologie Végétale, CP 206/2, Faculté des Sciences, Université Libre de Bruxelles, Bld du Triomphe, B-1050 Brussels, Belgium
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26
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Prévost M, Jacquemotte F, Oberg KA, Staelens D, Devreese B, Van Beeumen J. Conformational variability of the synthetic peptide 129-141 of the mouse prion protein. J Biomol Struct Dyn 2000; 18:237-48. [PMID: 11089645 DOI: 10.1080/07391102.2000.10506662] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Abstract
The effect of solution conditions on the conformation of the peptide corresponding to residues 129-141 of the mouse prion protein has been examined by experimental and theoretical tools including circular dichroism, secondary structure predictions, and Molecular Dynamics simulations. The conformational properties of the peptide observed by CD confirm the prediction results: the peptide is chiefly random coil in water. The conformational sampling performed by Molecular Dynamics simulations in water also corroborates the flexibility of the peptide, in particular for the N-terminal part. We show, however, that the peptide samples hairpin conformations in one of several approximately 1-ns Molecular Dynamics simulations in water. Interestingly, the analysis of the CD spectra obtained in this study suggests the presence of beta-structure which, given the length of the peptide, can only consist in beta-hairpin. The peptide can also be induced to form a modest percentage of helical structure in the presence of organic cosolvents such as trifluoroethanol, or detergents such as sodium dodecyl sulfate and lysophosphatidylcholine. This result is different from that obtained for a homologous hamster fragment, which differs from the mouse sequence by the single substitution of Ile 139 to Met. Interestingly, this substitution is crucial for the barrier in the transmission of the prion disease between hamsters and mice.
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Affiliation(s)
- M Prévost
- Ingénierie Biomoléculaire, Université Libre de Bruxelles, Belgium.
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27
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Dave N, Troullier A, Mus-Veteau I, Duñach M, Leblanc G, Padrós E. Secondary structure components and properties of the melibiose permease from Escherichia coli: a fourier transform infrared spectroscopy analysis. Biophys J 2000; 79:747-55. [PMID: 10920008 PMCID: PMC1300974 DOI: 10.1016/s0006-3495(00)76332-6] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The structure of the melibiose permease from Escherichia coli has been investigated by Fourier transform infrared spectroscopy, using the purified transporter either in the solubilized state or reconstituted in E. coli lipids. In both instances, the spectra suggest that the permease secondary structure is dominated by alpha-helical components (up to 50%) and contains beta-structure (20%) and additional components assigned to turns, 3(10) helix, and nonordered structures (30%). Two distinct and strong absorption bands are recorded at 1660 and 1653 cm(-1), i.e., in the usual range of absorption of helices of membrane proteins. Moreover, conditions that preserve the transporter functionality (reconstitution in liposomes or solubilization with dodecyl maltoside) make possible the detection of two separate alpha-helical bands of comparable intensity. In contrast, a single intense band, centered at approximately 1656 cm(-1), is recorded from the inactive permease in Triton X-100, or a merged and broader signal is recorded after the solubilized protein is heated in dodecyl maltoside. It is suggested that in the functional permease, distinct signals at 1660 and 1653 cm(-1) arise from two different populations of alpha-helical domains. Furthermore, the sodium- and/or melibiose-induced changes in amide I line shape, and in particular, in the relative amplitudes of the 1660 and 1653 cm(-1) bands, indicate that the secondary structure is modified during the early step of sugar transport. Finally, the observation that approximately 80% of the backbone amide protons can be exchanged suggests high conformational flexibility and/or a large accessibility of the membrane domains to the aqueous solvent.
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Affiliation(s)
- N Dave
- Unitat de Biofísica, Departament de Bioquímica i de Biologia Molecular, Facultat de Medicina, Universitat Autònoma de Barcelona, Bellaterra, Barcelona 08193, Spain
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28
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de Groot BL, Heymann JB, Engel A, Mitsuoka K, Fujiyoshi Y, Grubmüller H. The fold of human aquaporin 1. J Mol Biol 2000; 300:987-94. [PMID: 10891283 DOI: 10.1006/jmbi.2000.3913] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The fold of human aquaporin 1 is determined from cryo-electron microscopic data at 4.5 A resolution. The monomeric structure consists of two transmembrane triple helices arranged around a pseudo-2-fold axis connected by a long flexible extracellular loop. Each triplet contains between its second and third helix a functional loop containing the highly conserved fingerprint NPA motif. These functional loops are assumed to fold inwards between the two triplets, thereby forming the heart of the water channel. The helix topology was determined from the directionality pattern of each of the six transmembrane helices with respect to the membrane, together with constraints defined by the sequence and atomic force microscopy data. The directionality of the helices was determined by collecting the best-fitting orientations resulting from a search through the three-dimensional experimental map for a large number of alpha-helical fragments. Tests on cryo-electron crystallographic bacteriorhodopsin data suggest that our method is generally applicable to determine the topology of helical proteins for which only medium-resolution electron microscopy data are available.
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Affiliation(s)
- B L de Groot
- Theoretical Molecular Biophysics Group, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, Göttingen, D-37077, Germany
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29
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Abstract
The high water permeability characteristic of mammalian red cell membranes is now known to be caused by the protein AQP1. This channel freely permits movement of water across the cell membrane, but it is not permeated by other small, uncharged molecules or charged solutes. AQP1 is a tetramer with each subunit containing an aqueous pore likened to an hourglass formed by obversely arranged tandem repeats. Cryoelectron microscopy of reconstituted AQP1 membrane crystals has revealed the three-dimensional structure at 3-6 A. AQP1 is distributed in apical and basolateral membranes of renal proximal tubules and descending thin limbs as well as capillary endothelia. Ten mammalian aquaporins have been identified in water-permeable tissues and fall into two groupings. Orthodox aquaporins are water-selective and include AQP2, a vasopressin-regulated water channel in renal collecting duct, in addition to AQP0, AQP4, and AQP5. Multifunctional aquaglyceroporins AQP3, AQP7, and AQP9 are permeated by water, glycerol, and some other solutes. Aquaporins are being defined in numerous other species including amphibia, insects, plants, and microbials. Members of the aquaporin family are implicated in numerous physiological processes as well as the pathophysiology of a wide range of clinical disorders.
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Affiliation(s)
- M Borgnia
- Department of Biological Chemistry, Johns Hopkins School of Medicine, Baltimore, Maryland 21205-2185, USA
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30
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Affiliation(s)
- Peter Agre
- Departments of Biological Chemistry and Medicine, Johns Hopkins School of Medicine, Baltimore, Maryland
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31
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Khurana R, Fink AL. Do parallel beta-helix proteins have a unique fourier transform infrared spectrum? Biophys J 2000; 78:994-1000. [PMID: 10653812 PMCID: PMC1300702 DOI: 10.1016/s0006-3495(00)76657-4] [Citation(s) in RCA: 100] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
Several polypeptides have been found to adopt an unusual domain structure known as the parallel beta-helix. These domains are characterized by parallel beta-strands, three of which form a single parallel beta-helix coil, and lead to long, extended beta-sheets. We have used ATR-FTIR (attenuated total reflectance-fourier transform infrared spectroscopy) to analyze the secondary structure of representative examples of this class of protein. Because the three-dimensional structures of parallel beta-helix proteins are unique, we initiated this study to determine if there was a corresponding unique FTIR signal associated with the parallel beta-helix conformation. Analysis of the amide I region, emanating from the carbonyl stretch vibration, reveals a strong absorbance band at 1638 cm(-1) in each of the parallel beta-helix proteins. This band is assigned to the parallel beta-sheet structure. However, components at this frequency are also commonly observed for beta-sheets in many classes of globular proteins. Thus we conclude that there is no unique infrared signature for parallel beta-helix structure. Additional contributions in the 1638 cm(-1) region, and at lower frequencies, were ascribed to hydrogen bonding between the coils in the loop/turn regions and amide side-chain interactions, respectively. A 13-residue peptide that forms fibrils and has been proposed to form beta-helical structure was also examined, and its FTIR spectrum was compared to that of the parallel beta-helix proteins.
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Affiliation(s)
- R Khurana
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, California 95064, USA
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32
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Abstract
The aquaporins (AQPs) are a family of small membrane-spanning proteins (monomer size approximately 30 kDa) that are expressed at plasma membranes in many cells types involved in fluid transport. This review is focused on the molecular structure and function of mammalian aquaporins. Basic features of aquaporin structure have been defined using mutagenesis, epitope tagging, and spectroscopic and freeze-fracture electron microscopy methods. Aquaporins appear to assemble in membranes as homotetramers in which each monomer, consisting of six membrane-spanning alpha-helical domains with cytoplasmically oriented amino and carboxy termini, contains a distinct water pore. Medium-resolution structural analysis by electron cryocrystallography indicated that the six tilted helical segments form a barrel surrounding a central pore-like region that contains additional protein density. Several of the mammalian aquaporins (e.g., AQP1, AQP2, AQP4, and AQP5) appear to be highly selective for the passage of water, whereas others (recently termed aquaglyceroporins) also transport glycerol (e.g., AQP3 and AQP8) and even larger solutes (AQP9). Evidence for possible movement of ions and carbon dioxide through the aquaporins is reviewed here, as well as evidence for direct regulation of aquaporin function by posttranslational modification such as phosphorylation. Important unresolved issues include definition of the molecular pathway through which water and solutes move, the nature of monomer-monomer interactions, and the physiological significance of aquaporin-mediated solute movement. Recent results from knockout mice implicating multiple physiological roles of aquaporins suggest that the aquaporins may be suitable targets for drug discovery by structure-based and/or high-throughput screening strategies.
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Affiliation(s)
- A S Verkman
- Departments of Medicine and Physiology, Cardiovascular Research Institute, University of California, San Francisco 94143-0521, USA.
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33
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Arrondo JL, Goñi FM. Structure and dynamics of membrane proteins as studied by infrared spectroscopy. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 1999; 72:367-405. [PMID: 10605294 DOI: 10.1016/s0079-6107(99)00007-3] [Citation(s) in RCA: 322] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Infrared (IR) spectroscopy is a useful technique in the study of protein conformation and dynamics. The possibilities of the technique become apparent specially when applied to large proteins in turbid suspensions, as is often the case with membrane proteins. The present review describes the applications of IR spectroscopy to the study of membrane proteins, with an emphasis on recent work and on spectra recorded in the transmission mode, rather than using reflectance techniques. Data treatment procedures are discussed, including band analysis and difference spectroscopy methods. A technique for the analysis of protein secondary and tertiary structures that combines band analysis by curve-fitting of original spectra with protein thermal denaturation is described in detail. The assignment of IR protein bands in H2O and in D2O, one of the more difficult points in protein IR spectroscopy, is also reviewed, including some cases of unclear assignments such as loops, beta-hairpins, or 3(10)-helices. The review includes monographic studies of some membrane proteins whose structure and function have been analysed in detail by IR spectroscopy. Special emphasis has been made on the role of subunit III in cytochrome c oxidase structure, and the proton pathways across this molecule, on the topology and functional cycle of sarcoplasmic reticulum Ca(2+)-ATPase, and on the role of lipids in determining the structure of the nicotinic acetylcholine receptor. In addition, shorter descriptions of retinal proteins and references to other membrane proteins that have been studied less extensively are also included.
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Affiliation(s)
- J L Arrondo
- Unidad de Biofísica (Centro Mixto CSIC-UPV/EHU), Bilbao, Spain.
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34
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Goormaghtigh E, Raussens V, Ruysschaert JM. Attenuated total reflection infrared spectroscopy of proteins and lipids in biological membranes. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1422:105-85. [PMID: 10393271 DOI: 10.1016/s0304-4157(99)00004-0] [Citation(s) in RCA: 452] [Impact Index Per Article: 18.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Affiliation(s)
- E Goormaghtigh
- Laboratoire de Chimie-Physique des Macromolécules aux Interfaces, P. O. Box 206/2, Université Libre de Bruxelles, Campus Plaine, B-1050, Brussels, Belgium.
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35
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Nielsen S, Kwon TH, Christensen BM, Promeneur D, Frøkiaer J, Marples D. Physiology and pathophysiology of renal aquaporins. J Am Soc Nephrol 1999; 10:647-63. [PMID: 10073616 DOI: 10.1681/asn.v103647] [Citation(s) in RCA: 210] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
The discovery of aquaporin membrane water channels by Agre and coworkers answered a long-standing biophysical question of how water specifically crosses biologic membranes, and provided insight, at the molecular level, into the fundamental physiology of water balance and the pathophysiology of water balance disorders. Of nine aquaporin isoforms, at least six are known to be present in the kidney at distinct sites along the nephron and collecting duct. Aquaporin-1 (AQP1) is extremely abundant in the proximal tubule and descending thin limb, where it appears to provide the chief route for proximal nephron water reabsorption. AQP2 is abundant in the collecting duct principal cells and is the chief target for vasopressin to regulate collecting duct water reabsorption. Acute regulation involves vasopressin-regulated trafficking of AQP2 between an intracellular reservoir and the apical plasma membrane. In addition, AQP2 is involved in chronic/adaptational regulation of body water balance achieved through regulation of AQP2 expression. Importantly, multiple studies have now identified a critical role of AQP2 in several inherited and acquired water balance disorders. This concerns inherited forms of nephrogenic diabetes insipidus and several, much more common acquired types of nephrogenic diabetes insipidus where AQP2 expression and/or targeting are affected. Conversely, AQP2 expression and targeting appear to be increased in some conditions with water retention such as pregnancy and congestive heart failure. AQP3 and AQP4 are basolateral water channels located in the kidney collecting duct, and AQP6 and AQP7 appear to be expressed at lower abundance at several sites including the proximal tubule. This review focuses mainly on the role of AQP2 in water balance regulation and in the pathophysiology of water balance disorders.
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Affiliation(s)
- S Nielsen
- Department of Cell Biology, Institute of Anatomy, University of Aarhus, Denmark.
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36
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Zhuang J, Privé GG, Werner GE, Ringler P, Kaback HR, Engel A. Two-dimensional crystallization of Escherichia coli lactose permease. J Struct Biol 1999; 125:63-75. [PMID: 10196117 DOI: 10.1006/jsbi.1998.4059] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
A chimeric protein consisting of lactose permease with cytochrome b562 in the middle cytoplasmic loop and six His residues at the C terminus (LacY/L6cytb562/417H6 or "red permease") was overexpressed in Escherichia coli and isolated by nickel affinity chromatography after solubilization with dodecyl-beta,d-maltopyranoside. Red permease was then reconstituted in the presence of phospholipids, yielding densely packed vesicles and well-ordered two-dimensional (2D) crystals as shown by electron microscopy of negatively stained specimens. Single-particle analysis of 16 383 protein particles in densely packed vesicles reveals a 5.4-nm-long trapeziform protein of 4.1 to 5.1 nm width, with a central stain-filled indentation. Depending on reconstitution conditions, trigonal and rectangular crystallographic packing arrangements of these elongated particles assembled into trimers are observed. The best ordered 2D crystals exhibit a rectangular unit cell, of dimensions a = 9.9 nm, b = 17.4 nm, that houses two trimeric complexes. Projection maps calculated to a resolution of 2 nm show that these crystals consist of two layers.
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Affiliation(s)
- J Zhuang
- M. E. Müller-Institute for Microscopy at the Biozentrum, University of Basel, Klingelbergstrasse 70, Basel, CH-4056, Switzerland
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37
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Pancoska P, Janota V, Keiderling TA. Novel matrix descriptor for secondary structure segments in proteins: demonstration of predictability from circular dichroism spectra. Anal Biochem 1999; 267:72-83. [PMID: 9918657 DOI: 10.1006/abio.1998.2960] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
An extension to standard protein secondary structure predictions using optical spectra that encompasses the number and average lengths of segments of uniform secondary structure in the sequence is demonstrated. The connectivity and numbers of segments can be described by a matrix descriptor [sij] (i, j representing segment types such as helix and beta-sheet strands). Independent knowledge of the fractional concentration of each secondary structure type and of the total number of residues in the protein then with [sij] yields the average segment length of each type. The physical background for prediction of this extended structural descriptor from spectral data is summarized, rules for its generation from reference X-ray structures are defined, and formal variants of its form are discussed. Using a novel neural network approach to analyze a training set of electronic circular dichroism (ECD) and vibrational circular dichroism (VCD) spectra for 23 proteins, matrix descriptors encompassing helix, sheet, and other forms are predicted. The results show that the matrix descriptor can be predicted to an accuracy comparable to that of conventionally predicted average fractional secondary structures. In this respect the ECD predictions of [sij] were significantly more accurate than the VCD ones, which may result from the longer range length dependence of the ECD bandshape and intensity. Summary results for a parallel analysis using Fourier transform infrared spectra indicate somewhat lower reliability than those for VCD.
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Affiliation(s)
- P Pancoska
- Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, M/C 111, Chicago, Illinois, 60607-7061, USA
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38
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Tamás MJ, Luyten K, Sutherland FC, Hernandez A, Albertyn J, Valadi H, Li H, Prior BA, Kilian SG, Ramos J, Gustafsson L, Thevelein JM, Hohmann S. Fps1p controls the accumulation and release of the compatible solute glycerol in yeast osmoregulation. Mol Microbiol 1999; 31:1087-104. [PMID: 10096077 DOI: 10.1046/j.1365-2958.1999.01248.x] [Citation(s) in RCA: 305] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The accumulation of compatible solutes, such as glycerol, in the yeast Saccharomyces cerevisiae, is a ubiquitous mechanism in cellular osmoregulation. Here, we demonstrate that yeast cells control glycerol accumulation in part via a regulated, Fps1p-mediated export of glycerol. Fps1p is a member of the MIP family of channel proteins most closely related to the bacterial glycerol facilitators. The protein is localized in the plasma membrane. The physiological role of Fps1p appears to be glycerol export rather than uptake. Fps1 delta mutants are sensitive to hypo-osmotic shock, demonstrating that osmolyte export is required for recovery from a sudden drop in external osmolarity. In wild-type cells, the glycerol transport rate is decreased by hyperosmotic shock and increased by hypo-osmotic shock on a subminute time scale. This regulation seems to be independent of the known yeast osmosensing HOG and PKC signalling pathways. Mutants lacking the unique hydrophilic N-terminal domain of Fps1p, or certain parts thereof, fail to reduce the glycerol transport rate after a hyperosmotic shock. Yeast cells carrying these constructs constitutively release glycerol and show a dominant hyperosmosensitivity, but compensate for glycerol loss after prolonged incubation by glycerol overproduction. Fps1p may be an example of a more widespread class of regulators of osmoadaptation, which control the cellular content and release of compatible solutes.
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Affiliation(s)
- M J Tamás
- Laboratorium voor Moleculaire Celbiologie, Katholieke Universiteit Leuven, Flanders, Belgium
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39
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Nielsen S, Frør J, Knepper MA. Renal aquaporins: key roles in water balance and water balance disorders. Curr Opin Nephrol Hypertens 1998; 7:509-16. [PMID: 9818197 DOI: 10.1097/00041552-199809000-00005] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The discovery of a family of molecular water channels, aquaporins, by Agre and co-workers has shed light on the long-standing biophysical question of how water traverses biological membranes, and has provided detailed molecular insight into the fundamental physiology of water balance and the pathophysiology of water balance disorders. In this review, we focus mainly on the vasopressin-regulated water channel, aquaporin 2, and its critical role in acute and chronic regulation of body water balance, as well as in multiple water balance disorders.
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Affiliation(s)
- S Nielsen
- Department of Cell Biology, University of Aarhus, Denmark.
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40
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Abstract
Life exists in water as universal solvent, and cells need to deal with its influx and efflux. Nature has accomplished the almost impossible, creating membrane channels with both a high flux and a high specificity for water. The first water channel was discovered in red blood cell membranes. Today known as aquaporin-1, this channel was found to be closely related to the major integral protein (MIP)1 of the eye lens. Cloning and sequencing of numerous related proteins of the MIP family revealed the widespread occurrence of such channels, suggesting an essential physiological function. Their structures hold the clues to the remarkable water channel activity, as well as to the arrangement of transmembrane segments in general. Recent medium-resolution three-dimensional electron microscopic studies determined a tetrameric complex with six tilted transmembrane helices per monomer. The helices within each monomer surround a central density formed by two interhelical loops implicated by mutagenesis in the water channel function. A combination of sequence analysis and assignment of the observed densities to predicted helices provides a basis for speculation on the nature of the water course through the protein. In particular, four highly conserved polar residues, E142-N192-N76-E17, are proposed to form a chain of key groups involved in the pathway of water flow through the channel.
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Affiliation(s)
- J B Heymann
- M. E. Müller-Institute for Microscopic Structural Biology, Biozentrum, University of Basel, Switzerland
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41
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Forato LA, Bernardes-Filho R, Colnago LA. Protein structure in KBr pellets by infrared spectroscopy. Anal Biochem 1998; 259:136-41. [PMID: 9606154 DOI: 10.1006/abio.1998.2599] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In this work we analyzed the secondary structure of 13 globular proteins in KBr pellet through Fourier transform infrared spectroscopy (FTIR). The quantification was based in singular value decomposition (SVD) theory, a pattern recognition method. The results show better correlation for alpha helix (0.90) and beta sheet (0.84) in amide I band, similar to the results obtained for proteins in solution. These results show that the protein secondary structure is conserved in solid state, in opposition to the results observed by FTIR using resolution enhancement techniques. The SVD analysis also show that in KBr pellets the protein secondary structures have absorbances in different wavenumbers when compared to those in solution. In this way, the use of KBr pellet and the pattern recognition method can be an ideal method to analyze protein secondary structure by FTIR.
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Affiliation(s)
- L A Forato
- Instituto de Química de São Carlos, Universidade de São Paulo, Brazil
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