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Zhuang J, Shang Q, Rastinejad F, Wu D. Decoding Allosteric Control in Hypoxia-Inducible Factors. J Mol Biol 2024; 436:168352. [PMID: 37935255 DOI: 10.1016/j.jmb.2023.168352] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2023] [Revised: 10/10/2023] [Accepted: 11/01/2023] [Indexed: 11/09/2023]
Abstract
The mammalian family of basic helix-loop-helix-PER-ARNT-SIM (bHLH-PAS) transcription factors possess the ability to sense and respond to diverse environmental and physiological cues. These proteins all share a common structural framework, comprising a bHLH domain, two PAS domains, and transcriptional activation or repression domain. To function effectively as transcription factors, members of the family must form dimers, bringing together bHLH segments to create a functional unit that allows for DNA response element binding. The significance of bHLH-PAS family is underscored by their involvement in many major human diseases, offering potential avenues for therapeutic intervention. Notably, the clear identification of ligand-binding cavities within their PAS domains enables the development of targeted small molecules. Two examples are Belzutifan, targeting hypoxia-inducible factor (HIF)-2α, and Tapinarof, targeting the aryl hydrocarbon receptor (AHR), both of which have gained regulatory approval recently. Here, we focus on the HIF subfamily. The crystal structures of all three HIF-α proteins have been elucidated, revealing their bHLH and tandem PAS domains are used to engage their dimerization partner aryl hydrocarbon receptor nuclear translocator (ARNT, also called HIF-1β). A broad range of recent findings point to a shared allosteric modulation mechanism among these proteins, whereby small-molecules at the PAS-B domains exert direct influence over the HIF-α transcriptional functions. As our understanding of the architectural and allosteric mechanisms of bHLH-PAS proteins continues to advance, the possibility of discovering new therapeutic drugs becomes increasingly promising.
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Affiliation(s)
- Jingjing Zhuang
- Marine College, Shandong University, Weihai 264209, China; Helmholtz International Lab, State Key Laboratory of Microbial Technology, Shandong University, Qingdao 266237, China
| | - Qinghong Shang
- Helmholtz International Lab, State Key Laboratory of Microbial Technology, Shandong University, Qingdao 266237, China
| | - Fraydoon Rastinejad
- Target Discovery Institute, Nuffield Department of Medicine Research Building, University of Oxford, Old Road Campus, Oxford OX3 7FZ, UK.
| | - Dalei Wu
- Helmholtz International Lab, State Key Laboratory of Microbial Technology, Shandong University, Qingdao 266237, China.
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Rastinejad F. The protein architecture and allosteric landscape of HNF4α. Front Endocrinol (Lausanne) 2023; 14:1219092. [PMID: 37732120 PMCID: PMC10507258 DOI: 10.3389/fendo.2023.1219092] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/08/2023] [Accepted: 08/01/2023] [Indexed: 09/22/2023] Open
Abstract
Hepatocyte nuclear factor 4 alpha (HNF4α) is a multi-faceted nuclear receptor responsible for governing the development and proper functioning of liver and pancreatic islet cells. Its transcriptional functions encompass the regulation of vital metabolic processes including cholesterol and fatty acid metabolism, and glucose sensing and control. Various genetic mutations and alterations in HNF4α are associated with diabetes, metabolic disorders, and cancers. From a structural perspective, HNF4α is one of the most comprehensively understood nuclear receptors due to its crystallographically observed architecture revealing interconnected DNA binding domains (DBDs) and ligand binding domains (LBDs). This review discusses key properties of HNF4α, including its mode of homodimerization, its binding to fatty acid ligands, the importance of post-translational modifications, and the mechanistic basis for allosteric functions. The surfaces linking HNF4α's DBDs and LBDs create a convergence zone that allows signals originating from any one domain to influence distant domains. The HNF4α-DNA complex serves as a prime illustration of how nuclear receptors utilize individual domains for specific functions, while also integrating these domains to create cohesive higher-order architectures that allow signal responsive functions.
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Affiliation(s)
- Fraydoon Rastinejad
- Nuffield Department of Medicine, Target Discovery Institute (NDMRB), University of Oxford, Oxford, United Kingdom
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3
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Rastinejad F. Retinoic acid receptor structures: the journey from single domains to full-length complex. J Mol Endocrinol 2022; 69:T25-T36. [PMID: 36069789 DOI: 10.1530/jme-22-0113] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/22/2022] [Accepted: 09/07/2022] [Indexed: 11/08/2022]
Abstract
The retinoic acid receptors (RARα, β, and γ) are multi-domain polypeptides that heterodimerize with retinoid X receptors (RXRα, β, and γ) to form functional transcription factors. Understanding the three-dimensional molecular organization of these nuclear receptors (NRs) began with RAR and RXR DNA-binding domains (DBDs), and were followed with studies on isolated ligand-binding domains (LBDs). The more complete picture emerged in 2017 with the multi-domain crystal structure of RXRα-RARβ on its response element with retinoic acid molecules and coactivator segments on both proteins. The analysis of that structure and its complementary studies have clarified the direct communication pathways within RXR-RAR polypeptides, through which DNA binding, protein-ligand, and protein-protein interactions are integrated for overall functional responses. Understanding the molecular connections in the RXR-RAR complex has benefited from direct observations of the multi-domain structures of RXRα-PPARγ, RXRα-LXRβ, HNF-4α homodimer, and androgen receptor homodimer, each bound to its response element. These comprehensive NR structures show unique quaternary architectures, yet all have DBD-DBD, LBD-LBD, and DBD-LBD domain-domain contacts within them. These convergence zones allow signals from discrete domains of their polypeptides to be propagated and integrated across their entire complex, shaping their overall responses in an allosteric fashion.
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Affiliation(s)
- Fraydoon Rastinejad
- Nuffield Department of Medicine, University of Oxford, Target Discovery Institute (NDM RB), Oxford, UK
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4
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Bedia C, Badia M, Muixí L, Levade T, Tauler R, Sierra A. GM2-GM3 gangliosides ratio is dependent on GRP94 through down-regulation of GM2-AP cofactor in brain metastasis cells. Sci Rep 2019; 9:14241. [PMID: 31578452 PMCID: PMC6775165 DOI: 10.1038/s41598-019-50761-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2019] [Accepted: 09/13/2019] [Indexed: 01/09/2023] Open
Abstract
GRP94 is an ATP-dependent chaperone able to regulate pro-oncogenic signaling pathways. Previous studies have shown a critical role of GRP94 in brain metastasis (BrM) pathogenesis and progression. In this work, an untargeted lipidomic analysis revealed that some lipid species were altered in GRP94-deficient cells, specially GM2 and GM3 gangliosides. The catalytic pathway of GM2 is affected by the low enzymatic activity of β-Hexosaminidase (HexA), responsible for the hydrolysis of GM2 to GM3. Moreover, a deficiency of the GM2-activator protein (GM2-AP), the cofactor of HexA, is observed without alteration of gene expression, indicating a post-transcriptional alteration of GM2-AP in the GRP94-ablated cells. One plausible explanation of these observations is that GM2-AP is a client of GRP94, resulting in defective GM2 catabolic processing and lysosomal accumulation of GM2 in GRP94-ablated cells. Overall, given the role of gangliosides in cell surface dynamics and signaling, their imbalance might be linked to modifications of cell behaviour acquired in BrM progression. This work indicates that GM2-AP could be an important factor in ganglioside balance maintenance. These findings highlight the relevance of GM3 and GM2 gangliosides in BrM and reveal GM2-AP as a promising diagnosis and therapeutic target in BrM research.
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Affiliation(s)
- Carmen Bedia
- Laboratory of Molecular and Translational Oncology, Institut d'Investigacions Biomèdiques August Pi i Sunyer-IDIBAPS, Centre de Recerca Biomèdica CELLEX, Barcelona, E-08036, Spain.
- Department of Environmental Chemistry, Institute of Environmental Assessment and Water Research (IDAEA-CSIC), Barcelona, Spain.
| | - Miriam Badia
- Laboratory of Molecular and Translational Oncology, Institut d'Investigacions Biomèdiques August Pi i Sunyer-IDIBAPS, Centre de Recerca Biomèdica CELLEX, Barcelona, E-08036, Spain
| | - Laia Muixí
- Biological Clues of the Invasive and Metastatic Phenotype Group, Bellvitge Biomedical Research Institute (IDIBELL), L'Hospitalet de Llobregat, Barcelona, E-08908, Spain
| | - Thierry Levade
- INSERM UMR 1037, Centre de Recherches en Cancérologie de Toulouse (CRCT), 31037, Toulouse, France
| | - Romà Tauler
- Department of Environmental Chemistry, Institute of Environmental Assessment and Water Research (IDAEA-CSIC), Barcelona, Spain
| | - Angels Sierra
- Laboratory of Molecular and Translational Oncology, Institut d'Investigacions Biomèdiques August Pi i Sunyer-IDIBAPS, Centre de Recerca Biomèdica CELLEX, Barcelona, E-08036, Spain
- Centre d'Estudis Sanitaris i Socials-CESS, University of Vic - Central University of Catalonia (UVic-UCC), Vic, E-08500, Spain
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5
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Carter JD, Mathias JD, Gomez EF, Ran Y, Xu F, Galiano L, Tran NQ, D'Amore PW, Wright CS, Chakravorty DK, Fanucci GE. Characterizing solution surface loop conformational flexibility of the GM2 activator protein. J Phys Chem B 2014; 118:10607-17. [PMID: 25127419 PMCID: PMC4161144 DOI: 10.1021/jp505938t] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
![]()
GM2AP
has a β-cup topology with numerous X-ray structures
showing multiple conformations for some of the surface loops, revealing
conformational flexibility that may be related to function, where
function is defined as either membrane binding associated with ligand
binding and extraction or interaction with other proteins. Here, site-directed
spin labeling (SDSL) electron paramagnetic resonance (EPR) spectroscopy
and molecular dynamic (MD) simulations are used to characterize the
mobility and conformational flexibility of various structural regions
of GM2AP. A series of 10 single cysteine amino acid substitutions
were generated, and the constructs were chemically modified with the
methanethiosulfonate spin label. Continuous wave (CW) EPR line shapes
were obtained and subsequently simulated using the microscopic order
macroscopic disorder (MOMD) program. Line shapes for sites that have
multiple conformations in the X-ray structures required two spectral
components, whereas spectra of the remaining sites were adequately
fit with single-component parameters. For spin labeled sites L126C
and I66C, spectra were acquired as a function of temperature, and
simulations provided for the determination of thermodynamic parameters
associated with conformational change. Binding to GM2 ligand did not
alter the conformational flexibility of the loops, as evaluated by
EPR and NMR spectroscopies. These results confirm that the conformational
flexibility observed in the surface loops of GM2AP crystals is present
in solution and that the exchange is slow on the EPR time scale (>ns).
Furthermore, MD simulation results are presented and agree well with
the conformational heterogeneity revealed by SDSL.
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Affiliation(s)
- Jeffery D Carter
- Department of Chemistry, University of Florida , P.O. Box 117200, Gainesville, Florida 32611-7200, United States
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Kolter T. Ganglioside biochemistry. ISRN BIOCHEMISTRY 2012; 2012:506160. [PMID: 25969757 PMCID: PMC4393008 DOI: 10.5402/2012/506160] [Citation(s) in RCA: 109] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/18/2012] [Accepted: 10/09/2012] [Indexed: 01/21/2023]
Abstract
Gangliosides are sialic acid-containing glycosphingolipids. They occur especially on the cellular surfaces of neuronal cells, where they form a complex pattern, but are also found in many other cell types. The paper provides a general overview on their structures, occurrence, and metabolism. Key functional, biochemical, and pathobiochemical aspects are summarized.
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Affiliation(s)
- Thomas Kolter
- Program Unit Membrane Biology & Lipid Biochemistry, LiMES, University of Bonn, Gerhard-Domagk Straße 1, 53121 Bonn, Germany
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7
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Pikielny CW. Drosophila CheB proteins Involved in Gustatory Detection of Pheromones Are Related to a Human Neurodegeneration Factor. VITAMINS AND HORMONES 2010; 83:273-87. [DOI: 10.1016/s0083-6729(10)83011-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/24/2023]
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8
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Mathias JD, Ran Y, Carter JD, Fanucci GE. Interactions of the GM2 activator protein with phosphatidylcholine bilayers: a site-directed spin-labeling power saturation study. Biophys J 2009; 97:1436-44. [PMID: 19720032 DOI: 10.1016/j.bpj.2009.05.058] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2009] [Revised: 04/29/2009] [Accepted: 05/11/2009] [Indexed: 10/20/2022] Open
Abstract
The GM2 activator protein (GM2AP) is an accessory protein that is an essential component in the catabolism of the ganglioside GM2. A function of GM2AP is to bind and extract GM2 from intralysosomal vesicles, forming a soluble protein-lipid complex, which interacts with the hydrolase Hexosaminidase A, the enzyme that cleaves the terminal sugar group of GM2. Here, we used site-directed spin labeling with power saturation electron paramagnetic resonance to determine the surface-bound orientation of GM2AP upon phosphatidylcholine vesicles. Because GM2AP extracts lipid ligands from the vesicle and is undergoing exchange on and off the vesicle surface, we utilized a nickel-chelating lipid to localize the paramagnetic metal collider to the lipid bilayer-aqueous interface. Spin-labeled sites that collide with the lipid-bound metal relaxing agent provide a means for mapping sites of the protein that interact with the lipid bilayer interface. Results show that GM2AP binds to lipid bilayers such that the residues lining the lipid-binding cavity lie on the vesicle surface. This orientation creates a favorable microenvironment that can allow for the lipid tails to flip out of the bilayer directly into the hydrophobic pocket of GM2AP.
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Affiliation(s)
- Jordan D Mathias
- Department of Chemistry, University of Florida, Gainesville, Florida, USA
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9
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Kolter T, Sandhoff K. Lysosomal degradation of membrane lipids. FEBS Lett 2009; 584:1700-12. [PMID: 19836391 DOI: 10.1016/j.febslet.2009.10.021] [Citation(s) in RCA: 201] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2009] [Accepted: 10/09/2009] [Indexed: 01/05/2023]
Abstract
The constitutive degradation of membrane components takes place in the acidic compartments of a cell, the endosomes and lysosomes. Sites of lipid degradation are intralysosomal membranes that are formed in endosomes, where the lipid composition is adjusted for degradation. Cholesterol is sorted out of the inner membranes, their content in bis(monoacylglycero)phosphate increases, and, most likely, sphingomyelin is degraded to ceramide. Together with endosomal and lysosomal lipid-binding proteins, the Niemann-Pick disease, type C2-protein, the GM2-activator, and the saposins sap-A, -B, -C, and -D, a suitable membrane lipid composition is required for degradation of complex lipids by hydrolytic enzymes.
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Affiliation(s)
- Thomas Kolter
- LiMES - Life and Medical Sciences Institute, Membrane Biology and Lipid Biochemistry Unit, c/o Kekulé-Institut für Organische Chemie und Biochemie, University of Bonn, Bonn, Germany
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10
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Ligand extraction properties of the GM2 activator protein and its interactions with lipid vesicles. Biophys J 2009; 97:257-66. [PMID: 19580763 DOI: 10.1016/j.bpj.2009.03.065] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2008] [Revised: 03/25/2009] [Accepted: 03/31/2009] [Indexed: 11/23/2022] Open
Abstract
The GM2 activator protein (GM2AP) is an accessory protein required for the enzymatic conversion of GM2 to GM3 by hydrolases in the lysosomal compartments of cells. Here, GM2AP interactions with lipid vesicles are investigated by sucrose-loaded vesicle sedimentation and gel filtration assays, and the effects of pH and lipid composition on membrane binding and lipid extraction are characterized. The sedimentation experiments allow for facile quantification of the percentage of protein in solution and on the bilayer surface, with detailed analysis of the protein:lipid complex that remains in solution. Optimum binding and ligand extraction is found for pH 4.8 where <15% of the protein remains surface associated regardless of the lipid composition. In addition to extracting GM2, we find that GM2AP readily extracts dansyl-headgroup-labeled lipids as well as other phospholipids from vesicles. The ability of GM2AP to extract dansyl-DHPE from vesicles is altered by pH and the specific ligand GM2. Although the unique endosomal lipid, bis(monoacylglycero)phosphate, is not required for ligand extraction, it does enhance the extraction efficiency of GM2 when cholesterol is present in the vesicles.
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11
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Starostina E, Xu A, Lin H, Pikielny CW. A Drosophila protein family implicated in pheromone perception is related to Tay-Sachs GM2-activator protein. J Biol Chem 2008; 284:585-594. [PMID: 18952610 DOI: 10.1074/jbc.m806474200] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Low volatility, lipid-like cuticular hydrocarbon pheromones produced by Drosophila melanogaster females play an essential role in triggering and modulating mating behavior, but the chemosensory mechanisms involved remain poorly understood. Recently, we showed that the CheB42a protein, which is expressed in only 10 pheromone-sensing taste hairs on the front legs of males, modulates progression to late stages of male courtship behavior in response to female-specific cuticular hydrocarbons. Here we report that expression of all 12 genes in the CheB gene family is predominantly or exclusively gustatory-specific, and occurs in many different, often non-overlapping patterns. Only the Gr family of gustatory receptor genes displays a comparable variety of gustatory-specific expression patterns. Unlike Grs, however, expression of all but one CheB gene is sexually dimorphic. Like CheB42a, other CheBs may therefore function specifically in gustatory perception of pheromones. We also show that CheBs belong to the ML superfamily of lipid-binding proteins, and are most similar to human GM2-activator protein (GM2-AP). In particular, GM2-AP residues involved in ligand binding are conserved in CheBs but not in other ML proteins. Finally, CheB42a is specifically secreted into the inner lumen of pheromone-sensing taste hairs, where pheromones interact with membrane-bound receptors. We propose that CheB proteins interact directly with lipid-like Drosophila pheromones and modulate their detection by the gustatory signal transduction machinery. Furthermore, as loss of GM2-AP in Tay-Sachs disease prevents degradation of GM2 gangliosides and results in neurodegeneration, the function of CheBs in pheromone response may involve biochemical mechanisms critical for lipid metabolism in human neurons.
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Affiliation(s)
- Elena Starostina
- Department of Genetics and the Neuroscience Center, Dartmouth Medical School, Hanover, New Hampshire 03755; Department of Genetics and the Neuroscience Center, Dartmouth Medical School, Hanover, New Hampshire 03755
| | - Aiguo Xu
- Department of Genetics and the Neuroscience Center, Dartmouth Medical School, Hanover, New Hampshire 03755; Department of Genetics and the Neuroscience Center, Dartmouth Medical School, Hanover, New Hampshire 03755
| | - Heping Lin
- Department of Genetics and the Neuroscience Center, Dartmouth Medical School, Hanover, New Hampshire 03755; Department of Genetics and the Neuroscience Center, Dartmouth Medical School, Hanover, New Hampshire 03755
| | - Claudio W Pikielny
- Department of Genetics and the Neuroscience Center, Dartmouth Medical School, Hanover, New Hampshire 03755; Department of Genetics and the Neuroscience Center, Dartmouth Medical School, Hanover, New Hampshire 03755.
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12
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Wislet-Gendebien S, Visanji NP, Whitehead SN, Marsilio D, Hou W, Figeys D, Fraser PE, Bennett SAL, Tandon A. Differential regulation of wild-type and mutant alpha-synuclein binding to synaptic membranes by cytosolic factors. BMC Neurosci 2008; 9:92. [PMID: 18808659 PMCID: PMC2562387 DOI: 10.1186/1471-2202-9-92] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2008] [Accepted: 09/22/2008] [Indexed: 01/22/2023] Open
Abstract
BACKGROUND Alpha-Synuclein (alpha-syn), a 140 amino acid protein associated with presynaptic membranes in brain, is a major constituent of Lewy bodies in Parkinson's disease (PD). Three missense mutations (A30P, A53T and E46K) in the alpha-syn gene are associated with rare autosomal dominant forms of familial PD. However, the regulation of alpha-syn's cellular localization in neurons and the effects of the PD-linked mutations are poorly understood. RESULTS In the present study, we analysed the ability of cytosolic factors to regulate alpha-syn binding to synaptic membranes. We show that co-incubation with brain cytosol significantly increases the membrane binding of normal and PD-linked mutant alpha-syn. To characterize cytosolic factor(s) that modulate alpha-syn binding properties, we investigated the ability of proteins, lipids, ATP and calcium to modulate alpha-syn membrane interactions. We report that lipids and ATP are two of the principal cytosolic components that modulate Wt and A53T alpha-syn binding to the synaptic membrane. We further show that 1-O-hexadecyl-2-acetyl-sn-glycero-3-phosphocholine (C16:0 PAF) is one of the principal lipids found in complex with cytosolic proteins and is required to enhance alpha-syn interaction with synaptic membrane. In addition, the impaired membrane binding observed for A30P alpha-syn was significantly mitigated by the presence of protease-sensitive factors in brain cytosol. CONCLUSION These findings suggest that endogenous brain cytosolic factors regulate Wt and mutant alpha-syn membrane binding, and could represent potential targets to influence alpha-syn solubility in brain.
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Affiliation(s)
- Sabine Wislet-Gendebien
- Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, Ontario, M5S 3H2 Canada.
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Ohto U, Fukase K, Miyake K, Satow Y. Crystal structures of human MD-2 and its complex with antiendotoxic lipid IVa. Science 2007; 316:1632-4. [PMID: 17569869 DOI: 10.1126/science.1139111] [Citation(s) in RCA: 368] [Impact Index Per Article: 21.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Endotoxic lipopolysaccharide (LPS) with potent immunostimulatory activity is recognized by the receptor complex of MD-2 and Toll-like receptor 4. Crystal structures of human MD-2 and its complex with the antiendotoxic tetra-acylated lipid A core of LPS have been determined at 2.0 and 2.2 angstrom resolutions, respectively. MD-2 shows a deep hydrophobic cavity sandwiched by two beta sheets, in which four acyl chains of the ligand are fully confined. The phosphorylated glucosamine moieties are located at the entrance to the cavity. These structures suggest that MD-2 plays a principal role in endotoxin recognition and provide a basis for antiseptic drug development.
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Affiliation(s)
- Umeharu Ohto
- Graduate School of Pharmaceutical Sciences, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
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14
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Yanai H, Yoshida H, Tomono Y, Tada N, Chiba H. The possible contribution of a general glycosphingolipid transporter, GM2 activator protein, to atherosclerosis. J Atheroscler Thromb 2007; 13:281-5. [PMID: 17192692 DOI: 10.5551/jat.13.281] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
We previously found that oxidized low-density lipoprotein (LDL) elevated the expression of mRNA of GalNAcbeta1-4[NeuNAcalpha2-3]Galbeta1-4Glc-Cer (GM2) ganglioside activator protein, in human monocyte-derived macrophages. Recently, GM2 activator protein has become known as a general glycosphingolipid transporter as well as a specific cofactor for the hydrolysis of GM2 ganglioside by lysosomal beta-hexosaminidase A. Accumulation of glycosphingolipids has been observed in the serum or aorta of atherosclerotic model animals and humans. The proliferation of aortic smooth muscle cells, elevation of LDL uptake by macrophages, interfering LDL clearance by the liver, and enhancement of platelet adhesion to collagen have been proposed as the underlying mechanisms of glycosphingolipid-mediated atherogenesis. The GM2 activator protein can bind, solubilize and transport a broad spectrum of lipid molecules, indicating that GM2 activator protein may function as a general intra- and inter-cellular lipid transport protein. Collectively, elevated levels of GM2 activator protein in the aorta may be another feature of human atherosclerosis.
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Affiliation(s)
- Hidekatsu Yanai
- Division of General Medicine, Department of Internal Medicine, Kashiwa Hospital, The Jikei University School of Medicine, Chiba, Japan.
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15
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Mancek-Keber M, Jerala R. Structural similarity between the hydrophobic fluorescent probe and lipid A as a ligand of MD-2. FASEB J 2006; 20:1836-42. [PMID: 16940155 DOI: 10.1096/fj.06-5862com] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Toll-like receptors (TLRs) belong to the family of pattern recognition receptors, as they recognize molecules sharing a broad structural pattern rather than a single defined structure. Bacterial LPS is recognized by MD-2, which is associated with the extracellular domain of TLR4. Understanding the molecular recognition pattern of MD-2 could lead to efficient inhibitors of the excessive LPS signaling needed for early treatment of sepsis. The effect of the acyl chain variability of lipid A on its biological activity indicates that in addition to electrostatic interactions, the recognition must also involve hydrophobic interactions. We show that the fluorescent hydrophobic probe bis-ANS binds to MD-2 with a dissociation constant in the 10 nanomolar range, both to glycosylated and to nonglycosylated MD-2, and requires its native conformation. The binding site of bis-ANS overlaps with the binding site of LPS and is in the proximity of the single tryptophan residue. Furthermore, photoincorporation of bis-ANS by UV light inhibits the ability of MD-2 to confer the LPS responsiveness to the TLR4-transfected HEK293 cell line. Our results show that the structural pattern recognized by MD-2 is defined by the hydrophobic patch and a pair of separated negative charges.
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Affiliation(s)
- Mateja Mancek-Keber
- Laboratory of Biotechnology, National Institute of Chemistry, Hajdrihova 19, 1000 Ljubljana, Slovenia
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16
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Bruce AF, Gares MP, Selkirk ME, Gounaris K. Functional characterisation of a nematode secreted GM2-activator protein. Mol Biochem Parasitol 2006; 147:224-9. [PMID: 16569450 DOI: 10.1016/j.molbiopara.2006.02.014] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2006] [Revised: 02/14/2006] [Accepted: 02/20/2006] [Indexed: 10/24/2022]
Abstract
We have identified a GM2-activator protein (GM2AP) with highly unusual properties secreted by the nematode parasite Trichinella spiralis. Expression in Pichia pastoris resulted in a hyperglycosylated protein of 28 kDa, but the 18 kDa native protein was not glycosylated. The parasite GM2AP does not facilitate degradation of GM2 ganglioside by N-acetyl-beta-hexosaminidase A, although it does inhibit phospholipase D activity. Lack of the former activity might be explained by the absence of a domain implicated in binding to hexosaminidase. In addition, and contrary to data on the human GM2AP, the nematode homologue does not inhibit platelet activating factor-induced calcium mobilisation in neutrophils, but actually enhances mediator-induced chemotaxis.
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Affiliation(s)
- Alexandra F Bruce
- Division of Cell and Molecular Biology, Biochemistry Building, Imperial College London, South Kensington Campus, London SW7 2AY, UK
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Wendeler M, Werth N, Maier T, Schwarzmann G, Kolter T, Schoeniger M, Hoffmann D, Lemm T, Saenger W, Sandhoff K. The enzyme-binding region of human GM2-activator protein. FEBS J 2006; 273:982-91. [PMID: 16478472 DOI: 10.1111/j.1742-4658.2006.05126.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
The GM2-activator protein (GM2AP) is an essential cofactor for the lysosomal degradation of ganglioside GM2 by beta-hexosaminidase A (HexA). It mediates the interaction between the water-soluble exohydrolase and its membrane-embedded glycolipid substrate at the lipid-water interface. Functional deficiencies in this protein result in a fatal neurological storage disorder, the AB variant of GM2 gangliosidosis. In order to elucidate this cofactor's mode of action and identify the surface region of GM2AP responsible for binding to HexA, we designed several variant forms of this protein and evaluated the consequences of these mutations for lipid- and enzyme-binding properties using a variety of biophysical and functional studies. The point mutants D113K, M117V and E123K showed a drastically decreased capacity to stimulate HexA-catalysed GM2 degradation. However, surface plasmon resonance (SPR) spectroscopy showed that the binding of these variants to immobilized lipid bilayers and their ability to solubilize lipids from anionic vesicles were the same as for the wild-type protein. In addition, a fluorescence resonance energy transfer (FRET)-based assay system showed that these variants had the same capacity as wild-type GM2AP for intervesicular lipid transfer from donor to acceptor liposomes. The concentration-dependent effect of these variants on hydrolysis of the synthetic substrate 4-methylumbelliferyl-2-acetamido-2-deoxy-6-sulfo-beta-D-glucopyranoside (MUGS) indicated a weakened association with the enzyme's alpha subunit. This identifies the protein region affected by these mutations, the single short alpha helix of GM2AP, as the major determinant for the interaction with the enzyme. These results further confirm that the function of GM2AP is not restricted to a biological detergent that simply disrupts the membrane structure or lifts the substrate out of the lipid plane. In contrast, our data argue in favour of the critical importance of distinct activator-hexosaminidase interactions for GM2 degradation, and corroborate the view that the activator/lipid complex represents the true substrate for the degrading enzyme.
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Affiliation(s)
- Michaela Wendeler
- Kekulé-Institut für Organische Chemie und Biochemie der Universität Bonn, Germany
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Ciaffoni F, Tatti M, Boe A, Salvioli R, Fluharty A, Sonnino S, Vaccaro AM. Saposin B binds and transfers phospholipids. J Lipid Res 2006; 47:1045-53. [PMID: 16461955 DOI: 10.1194/jlr.m500547-jlr200] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Saposin B (Sap B) is a member of a family of four small glycoproteins, Sap A, B, C, and D. Like the other three saposins, Sap B plays a physiological role in the lysosomal degradation of sphingolipids (SLs). Although the interaction of Sap B with SLs has been investigated extensively, that with the main membrane lipid components, namely phospholipids and cholesterol (Chol), is scarcely known. Using large unilamellar vesicles (LUVs) as membrane models, we have now found that Sap B simultaneously extracts from the lipid surface neutral [phosphatidylcholine (PC)] and anionic [phosphatidylinositol (PI)] phospholipids, fewer SLs [ganglioside GM1 (GM1) or cerebroside sulfate (CS)], and no Chol. More PI than SL (GM1 or CS) was solubilized from LUVs containing equal amounts of PI and SLs. An increase in PI level had a poor effect on the Sap B-induced solubilization of GM1 or CS but strongly inhibited that of PC. Sap B was able not only to bind, but also to transfer phospholipids between lipid surfaces. Both the phospholipid binding and transfer activities were optimal at low pH values. These results represent the first biochemical analysis of the Sap B interaction with phospholipids. The capacity of Sap B to bind and transfer phospholipids occurs under conditions mimicking the interior of the late endosomal/lysosomal compartment and thus might have physiological relevance.
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Affiliation(s)
- Fiorella Ciaffoni
- Department of Hematology, Oncology, and Molecular Medicine, Istituto Superiore Sanita, Roma, Italy
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Wright CS, Mi LZ, Lee S, Rastinejad F. Crystal Structure Analysis of Phosphatidylcholine−GM2-Activator Product Complexes: Evidence for Hydrolase Activity,. Biochemistry 2005; 44:13510-21. [PMID: 16216074 DOI: 10.1021/bi050668w] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
GM2-activator protein (GM2AP) is a lysosomal lipid transfer protein with important biological roles in ganglioside catabolism, phospholipid metabolism, and T-cell activation. Previous studies of crystal structures of GM2AP complexed with the physiological ligand GM2 and platelet activating factor (PAF) have shown binding at two specific locations within the spacious apolar pocket and an ordering effect of endogenous resident lipids. To investigate the structural basis of phospholipid binding further, GM2AP was cocrystallized with phosphatidylcholine (PC), known to interact with GM2AP. Analysis of three crystal forms revealed binding of single chain lipids and fatty acids only and surprisingly not intact PC. The regions of best defined electron density are consistent with the presence of lyso-PC and oleic acid, which constitute deacylation products of PC. Their acyl tails are in stacking contact with shorter, less well-defined stretches of electron density that may represent resident fatty acids. The GM2AP associated hydrolytic activity that generates lyso-PC was further confirmed by mass spectrometry and enzymatic assays. In addition, we report the structures of (i) mutant Y137S, assessing the role of Tyr137 in lipid transfer via the hydrophobic cleft, and (ii) apo-mouse GM2AP, revealing a hydrophobic pocket with a constricted opening. Our structural results provide new insights into the biological functions of GM2AP. The combined effect of hydrolytic and lipid transfer properties has profound implications in cellular signaling.
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Affiliation(s)
- Christine S Wright
- Department of Pharmacology, X-ray Crystallography Laboratory, University of Virginia, Charlottesville, Virginia 22908-0735, USA.
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Schwarzmann G, Wendeler M, Sandhoff K. Synthesis of novel NBD-GM1 and NBD-GM2 for the transfer activity of GM2-activator protein by a FRET-based assay system. Glycobiology 2005; 15:1302-11. [PMID: 16079415 DOI: 10.1093/glycob/cwj018] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The ganglioside-activator protein is an essential cofactor for the lysosomal degradation of ganglioside GM2 (GM2) by beta-hexosaminidase A. It mediates the interaction between the water-soluble exohydrolase and its membrane-embedded glycolipid substrate at the lipid-water interphase. Mutations in the gene encoding this glycoprotein result in a fatal neurological storage disorder, the AB variant of GM2-gangliosidosis. In order to efficiently and sensitively probe the glycolipid binding and membrane activity of this cofactor, we synthesized two new fluorescent glycosphingolipid (GSL) probes, 2-NBD-GM1 and 2-NBD-GM2. Both compounds were synthesized in a convergent and multistep synthesis starting from the respective gangliosides isolated from natural sources. The added functionality of 2-aminogangliosides allowed us to introduce the chromophore into the region between the polar head group and the hydrophobic anchor of the lipid. Both fluorescent glycolipids exhibited an extremely low off-rate in model membranes and displayed very efficient resonance energy transfer to rhodamine-dioleoyl phosphoglycerol ethanolamine (rhodamine-PE) as acceptor. The binding to GM2-activator protein (GM2AP) and the degrading enzyme was shown to be unaltered compared to their natural analogues. A novel fluorescence-resonance energy transfer (FRET) assay was developed to monitor in real time the protein-mediated intervesicular transfer of these lipids from donor to acceptor liposomes. The data obtained indicate that this rapid and robust system presented here should serve as a valuable tool to probe quantitatively and comprehensively the membrane activity of GM2AP and other sphingolipid activator proteins and facilitate further structure-function studies aimed at delineating independently the lipid- and the enzyme-binding mode of these essential cofactors.
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Affiliation(s)
- Günter Schwarzmann
- Kekulé-Institute für Organische Chemie und Biochemie, Gerhard-Domagk-Strasse 1, D-53121 Bonn, Germany.
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Johannessen BR, Skov LK, Kastrup JS, Kristensen O, Bolwig C, Larsen JN, Spangfort M, Lund K, Gajhede M. Structure of the house dust mite allergen Der f 2: implications for function and molecular basis of IgE cross-reactivity. FEBS Lett 2005; 579:1208-12. [PMID: 15710415 DOI: 10.1016/j.febslet.2004.11.115] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2004] [Revised: 11/23/2004] [Accepted: 11/24/2004] [Indexed: 11/21/2022]
Abstract
The X-ray structure of the group 2 major allergen from Dermatophagoides farinae (Der f 2) was determined to 1.83 A resolution. The overall Der f 2 structure comprises a single domain of immunoglobulin fold with two anti-parallel beta-sheets. A large hydrophobic cavity is formed in the interior of Der f 2. Structural comparisons to distantly related proteins suggest a role in lipid binding. Immunoglobulin E (IgE) cross-reactivity between group 2 house dust mite major allergens can be explained by conserved surface areas representing IgE binding epitopes.
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Affiliation(s)
- Birthe R Johannessen
- Biostructural Research, Department of Medicinal Chemistry, Danish University of Pharmaceutical Sciences, Universitetsparken 2, DK-2100 Copenhagen, Denmark
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