1
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Bera S, Fereiro JA, Saxena SK, Chryssikos D, Majhi K, Bendikov T, Sepunaru L, Ehre D, Tornow M, Pecht I, Vilan A, Sheves M, Cahen D. Near-Temperature-Independent Electron Transport Well beyond Expected Quantum Tunneling Range via Bacteriorhodopsin Multilayers. J Am Chem Soc 2023; 145. [PMID: 37933117 PMCID: PMC10655127 DOI: 10.1021/jacs.3c09120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2023] [Revised: 10/19/2023] [Accepted: 10/20/2023] [Indexed: 11/08/2023]
Abstract
A key conundrum of biomolecular electronics is efficient electron transport (ETp) through solid-state junctions up to 10 nm, often without temperature activation. Such behavior challenges known charge transport mechanisms, especially via nonconjugated molecules such as proteins. Single-step, coherent quantum-mechanical tunneling proposed for ETp across small protein, 2-3 nm wide junctions, but it is problematic for larger proteins. Here we exploit the ability of bacteriorhodopsin (bR), a well-studied, 4-5 nm long membrane protein, to assemble into well-defined single and multiple bilayers, from ∼9 to 60 nm thick, to investigate ETp limits as a function of junction width. To ensure sufficient signal/noise, we use large area (∼10-3 cm2) Au-protein-Si junctions. Photoemission spectra indicate a wide energy separation between electrode Fermi and the nearest protein-energy levels, as expected for a polymer of mostly saturated components. Junction currents decreased exponentially with increasing junction width, with uniquely low length-decay constants (0.05-0.5 nm-1). Remarkably, even for the widest junctions, currents are nearly temperature-independent, completely so below 160 K. While, among other things, the lack of temperature-dependence excludes, hopping as a plausible mechanism, coherent quantum-mechanical tunneling over 60 nm is physically implausible. The results may be understood if ETp is limited by injection into one of the contacts, followed by more efficient charge propagation across the protein. Still, the electrostatics of the protein films further limit the number of charge carriers injected into the protein film. How electron transport across dozens of nanometers of protein layers is more efficient than injection defines a riddle, requiring further study.
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Affiliation(s)
- Sudipta Bera
- Department
of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Jerry A. Fereiro
- Department
of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 7610001, Israel
- School
of Chemistry, Indian Institute of Science
Education and Research, Thiruvananthapuram 695551, Kerala, India
| | - Shailendra K. Saxena
- Department
of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 7610001, Israel
- Department
of Physics and Nanotechnology, College of Engineering and Technology, SRM Institute of Science and Technology, Kattankulathur, Chennai 603203, Tamil
Nadu, India
| | - Domenikos Chryssikos
- Molecular
Electronics, Technical University of Munich, 85748 Garching, Germany
- Fraunhofer
Institute for Electronic Microsystems and Solid State Technologies
(EMFT), 80686 München, Germany
| | - Koushik Majhi
- Department
of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Tatyana Bendikov
- Department
of Chemical Research Support, Weizmann Institute
of Science, Rehovot 7610001, Israel
| | - Lior Sepunaru
- Department
of Chemistry and Biochemistry, University
of California, Santa
Barbara, California 93106, United States
| | - David Ehre
- Department
of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Marc Tornow
- Molecular
Electronics, Technical University of Munich, 85748 Garching, Germany
- Fraunhofer
Institute for Electronic Microsystems and Solid State Technologies
(EMFT), 80686 München, Germany
| | - Israel Pecht
- Department
of Immunology and Regenerative Biology, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Ayelet Vilan
- Department
of Chemical and Biological Physics Weizmann
Institute of Science, Rehovot 7610001, Israel
| | - Mordechai Sheves
- Department
of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - David Cahen
- Department
of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 7610001, Israel
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2
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Kouyama T, Ihara K. Existence of two substates in the O intermediate of the bacteriorhodopsin photocycle. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2022; 1864:183998. [PMID: 35753392 DOI: 10.1016/j.bbamem.2022.183998] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2021] [Revised: 04/12/2022] [Accepted: 06/18/2022] [Indexed: 06/15/2023]
Abstract
The proton pumping cycle of bacteriorhodopsin (bR) is initiated when the retinal chromophore with the 13-trans configuration is photo-isomerized into the 13-cis configuration. To understand the recovery processes of the initial retinal configuration that occur in the late stage of the photocycle, we have performed a comprehensive analysis of absorption kinetics data collected at various pH levels and at different salt concentrations. The result of analysis revealed the following features of the late stages of the trans photocycle. i) Two substates occur in the O intermediate. ii) The visible absorption band of the first substate (O1) appears at a much shorter wavelength than that of the late substate (O2). iii) O1 is in rapid equilibrium with the preceding state (N), but O1 becomes less stable than N when an ionizable residue (X1) with a pKa value of 6.5 (in 2 M KCl) is deprotonated. iv) At a low pH and at a low salt concentration, the decay time constant of O2 is longer than those of the preceding states, but the relationship between these time constants is altered when the medium pH or the salt concentration is increased. On the basis of the present observations and previous studies on the structure of the chromophore in O, we suspect that the retinal chromophore in O1 takes on a distorted 13-cis configuration and the O1-to-O2 transition is accompanied by cis-to-trans isomerization about C13C14 bond.
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Affiliation(s)
- Tsutomu Kouyama
- Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan.
| | - Kunio Ihara
- Center for Gene Research, Nagoya University, Nagoya 464-8602, Japan
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3
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Shionoya T, Mizuno M, Kandori H, Mizutani Y. Contact-Mediated Retinal-Opsin Coupling Enables Proton Pumping in Gloeobacter Rhodopsin. J Phys Chem B 2022; 126:7857-7869. [PMID: 36173382 DOI: 10.1021/acs.jpcb.2c04208] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
When a chromophore embedded in a photoreceptive protein undergoes a reaction upon photoexcitation, the photoreaction triggers structural changes in the protein moiety that are necessary for the function of the protein. It is thus essential to elucidate the coupling between the chromophore and protein moiety to understand the functional mechanism for photoreceptive proteins, but the mechanism by which this coupling occurs remains poorly understood. Here, we show that nonbonded atomic contacts play an essential role in driving functionally important structural changes following photoisomerization of the chromophore in Gloeobacter rhodopsin (GR). Time-resolved ultraviolet resonance Raman spectroscopy revealed that the substitution of Trp222, which contacts with methyl groups of the retinal chromophore, with a Phe residue reduced the extent of structural change. The proton-pumping activity of the GR mutant was as small as 9% of that of the wild type. Time-resolved visible absorption and resonance Raman spectra showed that the photocycle of the mutant proceeded to the L intermediate following the all-trans to 13-cis photoisomerization step but did not result in the deprotonation of the chromophore. The present results demonstrate that the atomic contacts between the chromophore and the Trp222 side chain induce the structural changes necessary for proton transfer. The requirement for dense atomic packing in a protein structure for the efficient propagation of structural changes through a coupling mechanism is discussed.
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Affiliation(s)
- Tomomi Shionoya
- Department of Chemistry, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan
| | - Misao Mizuno
- Department of Chemistry, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan
| | - Hideki Kandori
- Department of Life Science and Applied Chemistry, Nagoya Institute of Technology, Showa-ku, Nagoya, Aichi 466-8555, Japan
| | - Yasuhisa Mizutani
- Department of Chemistry, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan
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4
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Miszta P, Pasznik P, Niewieczerzał S, Młynarczyk K, Filipek S. COGRIMEN: Coarse-Grained Method for Modeling of Membrane Proteins in Implicit Environments. J Chem Theory Comput 2022; 18:5145-5156. [PMID: 35998323 PMCID: PMC9476660 DOI: 10.1021/acs.jctc.2c00140] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
The presented methodology is based on coarse-grained
representation
of biomolecules in implicit environments and is designed for the molecular
dynamics simulations of membrane proteins and their complexes. The
membrane proteins are not only found in the cell membrane but also
in all membranous compartments of the cell: Golgi apparatus, mitochondria,
endosomes and lysosomes, and they usually form large complexes. To
investigate such systems the methodology is proposed based on two
independent approaches combining the coarse-grained MARTINI model
for proteins and the effective energy function to mimic the water/membrane
environments. The latter is based on the implicit environment developed
for all-atom simulations in the IMM1 method. The force field solvation
parameters for COGRIMEN were initially calculated from IMM1 all-atom
parameters and then optimized using Genetic Algorithms. The new methodology
was tested on membrane proteins, their complexes and oligomers. COGRIMEN
method is implemented as a patch for NAMD program and can be useful
for fast and brief studies of large membrane protein complexes.
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Affiliation(s)
- Przemysław Miszta
- Faculty of Chemistry, Biological and Chemical Research Centre, University of Warsaw, Warsaw 02-093, Poland
| | - Paweł Pasznik
- Faculty of Chemistry, Biological and Chemical Research Centre, University of Warsaw, Warsaw 02-093, Poland
| | - Szymon Niewieczerzał
- Faculty of Chemistry, Biological and Chemical Research Centre, University of Warsaw, Warsaw 02-093, Poland
| | - Krzysztof Młynarczyk
- Faculty of Chemistry, Biological and Chemical Research Centre, University of Warsaw, Warsaw 02-093, Poland
| | - Sławomir Filipek
- Faculty of Chemistry, Biological and Chemical Research Centre, University of Warsaw, Warsaw 02-093, Poland
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Abstract
Microbial rhodopsins are light-sensitive transmembrane proteins, evolutionary adapted by various organisms like archaea, bacteria, simple eukaryote, and viruses to utilize solar energy for their survival. A complete understanding of functional mechanisms of these proteins is not possible without the knowledge of their high-resolution structures, which can be primarily obtained by X-ray crystallography. This technique, however, requires high-quality crystals, growing of which is a great challenge especially in case of membrane proteins. In this chapter, we summarize methods applied for crystallization of microbial rhodopsins with the emphasis on crystallization in lipidic mesophases, also known as in meso approach. In particular, we describe in detail the methods of crystallization using lipidic cubic phase to grow both large crystals optimized for traditional crystallographic data collection and microcrystals for serial crystallography.
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Affiliation(s)
- Kirill Kovalev
- Institut de Biologie Structurale (IBS), Université Grenoble Alpes, CEA, CNRS, Grenoble, France
- Institute of Biological Information Processing (IBI-7: Structural Biochemistry), Forschungszentrum Jülich GmbH, Jülich, Germany
- JuStruct: Jülich Center for Structural Biology, Forschungszentrum Jülich GmbH, Jülich, Germany
- Research Center for Molecular Mechanisms of Aging and Age-Related Diseases, Moscow Institute of Physics and Technology (National Research University), Dolgoprudny, Russia
- Institute of Crystallography, University of Aachen (RWTH), Aachen, Germany
| | - Roman Astashkin
- Institut de Biologie Structurale (IBS), Université Grenoble Alpes, CEA, CNRS, Grenoble, France
| | - Valentin Gordeliy
- Institut de Biologie Structurale (IBS), Université Grenoble Alpes, CEA, CNRS, Grenoble, France
| | - Vadim Cherezov
- Bridge Institute, Department of Chemistry, University of Southern California, Los Angeles, CA, USA.
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6
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Polovinkin V, Khakurel K, Babiak M, Angelov B, Schneider B, Dohnalek J, Andreasson J, Hajdu J. Demonstration of electron diffraction from membrane protein crystals grown in a lipidic mesophase after lamella preparation by focused ion beam milling at cryogenic temperatures. J Appl Crystallogr 2020; 53:1416-1424. [PMID: 33304220 PMCID: PMC7710488 DOI: 10.1107/s1600576720013096] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2020] [Accepted: 09/27/2020] [Indexed: 12/26/2022] Open
Abstract
Electron diffraction experiments on crystals of membrane proteins grown in lipidic mesophases have not been possible owing to a thick layer of viscous crystallization medium around the crystals. Here it is shown that focused ion beam milling at cryogenic temperatures (cryo-FIB milling) can remove the viscous layer, and high-quality electron diffraction on a FIB-milled lamella of a bacteriorhodopsin 3D crystal is demonstrated. Electron crystallography of sub-micrometre-sized 3D protein crystals has emerged recently as a valuable field of structural biology. In meso crystallization methods, utilizing lipidic mesophases, particularly lipidic cubic phases (LCPs), can produce high-quality 3D crystals of membrane proteins (MPs). A major step towards realizing 3D electron crystallography of MP crystals, grown in meso, is to demonstrate electron diffraction from such crystals. The first task is to remove the viscous and sticky lipidic matrix that surrounds the crystals without damaging the crystals. Additionally, the crystals have to be thin enough to let electrons traverse them without significant multiple scattering. In the present work, the concept that focused ion beam milling at cryogenic temperatures (cryo-FIB milling) can be used to remove excess host lipidic mesophase matrix is experimentally verified, and then the crystals are thinned to a thickness suitable for electron diffraction. In this study, bacteriorhodopsin (BR) crystals grown in a lipidic cubic mesophase of monoolein were used as a model system. LCP from a part of a hexagon-shaped plate-like BR crystal (∼10 µm in thickness and ∼70 µm in the longest dimension), which was flash-frozen in liquid nitrogen, was milled away with a gallium FIB under cryogenic conditions, and a part of the crystal itself was thinned into a ∼210 nm-thick lamella with the ion beam. The frozen sample was then transferred into an electron cryo-microscope, and a nanovolume of ∼1400 × 1400 × 210 nm of the BR lamella was exposed to 200 kV electrons at a fluence of ∼0.06 e Å−2. The resulting electron diffraction peaks were detected beyond 2.7 Å resolution (with an average peak height to background ratio of >2) by a CMOS-based Ceta 16M camera. The results demonstrate that cryo-FIB milling produces high-quality lamellae from crystals grown in lipidic mesophases and pave the way for 3D electron crystallography on crystals grown or embedded in highly viscous media.
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Affiliation(s)
- Vitaly Polovinkin
- ELI Beamlines, Institute of Physics, Czech Academy of Science, Na Slovance 2, 18221 Prague, Czech Republic
| | - Krishna Khakurel
- ELI Beamlines, Institute of Physics, Czech Academy of Science, Na Slovance 2, 18221 Prague, Czech Republic
| | - Michal Babiak
- CEITEC - Central European Institute of Technology, Masaryk University, Kamenice 5/4, 62500 Brno, Czech Republic
| | - Borislav Angelov
- ELI Beamlines, Institute of Physics, Czech Academy of Science, Na Slovance 2, 18221 Prague, Czech Republic
| | - Bohdan Schneider
- Institute of Biotechnology of the Czech Academy of Sciences, BIOCEV, Prumyslova 595, CZ-252 50 Vestec, Czech Republic
| | - Jan Dohnalek
- Institute of Biotechnology of the Czech Academy of Sciences, BIOCEV, Prumyslova 595, CZ-252 50 Vestec, Czech Republic
| | - Jakob Andreasson
- ELI Beamlines, Institute of Physics, Czech Academy of Science, Na Slovance 2, 18221 Prague, Czech Republic
| | - Janos Hajdu
- ELI Beamlines, Institute of Physics, Czech Academy of Science, Na Slovance 2, 18221 Prague, Czech Republic.,Department of Cell and Molecular Biology, Uppsala University, Husargatan 3 (Box 596), SE-751 24 Uppsala, Sweden
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7
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Van Truong T, Ghosh M, Misra R, Krichevski O, Wachtel E, Friedman N, Sheves M, Patchornik G. Conjugation of native membranes via linear oligo-amines. Colloids Surf B Biointerfaces 2020; 193:111101. [DOI: 10.1016/j.colsurfb.2020.111101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2019] [Revised: 04/13/2020] [Accepted: 04/28/2020] [Indexed: 11/28/2022]
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8
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Van Truong T, Ghosh M, Wachtel E, Friedman N, Jung KH, Sheves M, Patchornik G. Promoting crystallization of intrinsic membrane proteins with conjugated micelles. Sci Rep 2020; 10:12199. [PMID: 32699228 PMCID: PMC7376161 DOI: 10.1038/s41598-020-68689-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2020] [Accepted: 06/29/2020] [Indexed: 11/09/2022] Open
Abstract
A new technique for promoting nucleation and growth of membrane protein (MP) crystals from micellar environments is reported. It relies on the conjugation of micelles that sequester MPs in protein detergent complexes (PDCs). Conjugation via amphiphilic [metal:chelator] complexes presumably takes place at the micelle/water interface, thereby bringing the PDCs into proximity, promoting crystal nucleation and growth. We have successfully applied this approach to two light-driven proton pumps: bacteriorhodopsin (bR) and the recently discovered King Sejong 1-2 (KS1-2), using the amphiphilic 4,4'-dinonyl-2,2'-dipyridyl (Dinonyl) (0.7 mM) chelator in combination with Zn2+, Fe2+, or Ni2+ (0.1 mM). Crystal growth in the presence of the [metal-chelator] complexes leads to purple, hexagonal crystals (50-75 µm in size) of bR or pink, rectangular/square crystals (5-15 µm) of KS1-2. The effects of divalent cation identity and concentration, chelator structure and concentration, ionic strength and pH on crystal size, morphology and process kinetics, are described.
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Affiliation(s)
- Thien Van Truong
- Department of Chemical Sciences, Ariel University, 40700, Ariel, Israel
| | - Mihir Ghosh
- Faculty of Chemistry, Weizmann Institute of Science, 76100, Rehovot, Israel
| | - Ellen Wachtel
- Faculty of Chemistry, Weizmann Institute of Science, 76100, Rehovot, Israel
| | - Noga Friedman
- Faculty of Chemistry, Weizmann Institute of Science, 76100, Rehovot, Israel
| | - Kwang-Hwan Jung
- Department of Life Science and Institute of Biological Interfaces, Sogang University, Seoul, 121-742, South Korea
| | - Mordechai Sheves
- Faculty of Chemistry, Weizmann Institute of Science, 76100, Rehovot, Israel
| | - Guy Patchornik
- Department of Chemical Sciences, Ariel University, 40700, Ariel, Israel.
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9
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X-ray structure analysis of bacteriorhodopsin at 1.3 Å resolution. Sci Rep 2018; 8:13123. [PMID: 30177765 PMCID: PMC6120890 DOI: 10.1038/s41598-018-31370-0] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2018] [Accepted: 08/13/2018] [Indexed: 11/12/2022] Open
Abstract
Bacteriorhodopsin (bR) of Halobacterium salinarum is a membrane protein that acts as a light-driven proton pump. bR and its homologues have recently been utilized in optogenetics and other applications. Although the structures of those have been reported so far, the resolutions are not sufficient for elucidation of the intrinsic structural features critical to the color tuning and ion pumping properties. Here we report the accurate crystallographic analysis of bR in the ground state. The influence of X-rays was suppressed by collecting the data under a low irradiation dose at 15 K. Consequently, individual atoms could be separately observed in the electron density map at better than 1.3 Å resolution. Residues from Thr5 to Ala233 were continuously constructed in the model. The twist of the retinal polyene was determined to be different from those in the previous models. Two conformations were observed for the proton release region. We discuss the meaning of these fine structural features.
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10
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Abstract
Microbial rhodopsins (MRs) are a large family of photoactive membrane proteins, found in microorganisms belonging to all kingdoms of life, with new members being constantly discovered. Among the MRs are light-driven proton, cation and anion pumps, light-gated cation and anion channels, and various photoreceptors. Due to their abundance and amenability to studies, MRs served as model systems for a great variety of biophysical techniques, and recently found a great application as optogenetic tools. While the basic aspects of microbial rhodopsins functioning have been known for some time, there is still a plenty of unanswered questions. This chapter presents and summarizes the available knowledge, focusing on the functional and structural studies.
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Affiliation(s)
- Ivan Gushchin
- Moscow Institute of Physics and Technology, Dolgoprudniy, Russia.
| | - Valentin Gordeliy
- Moscow Institute of Physics and Technology, Dolgoprudniy, Russia.
- University of Grenoble Alpes, CEA, CNRS, IBS, Grenoble, France.
- Institute of Complex Systems (ICS), ICS-6: Structural Biochemistry, Research Centre Jülich, Jülich, Germany.
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11
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Dong B, Sánchez-Magraner L, Luecke H. Structure of an Inward Proton-Transporting Anabaena Sensory Rhodopsin Mutant: Mechanistic Insights. Biophys J 2017; 111:963-72. [PMID: 27602724 DOI: 10.1016/j.bpj.2016.04.055] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2015] [Revised: 04/08/2016] [Accepted: 04/12/2016] [Indexed: 02/03/2023] Open
Abstract
Microbial rhodopsins are light-activated, seven-α-helical, retinylidene transmembrane proteins that have been identified in thousands of organisms across archaea, bacteria, fungi, and algae. Although they share a high degree of sequence identity and thus similarity in structure, many unique functions have been discovered and characterized among them. Some function as outward proton pumps, some as inward chloride pumps, whereas others function as light sensors or ion channels. Unique among the microbial rhodopsins characterized thus far, Anabaena sensory rhodopsin (ASR) is a photochromic sensor that interacts with a soluble 14-kDa cytoplasmic transducer that is encoded on the same operon. The sensor itself stably interconverts between all-trans-15-anti and 13-cis-15-syn retinal forms depending on the wavelength of illumination, although only the former participates in a photocycle with a signaling M intermediate. A mutation in the cytoplasmic half-channel of the protein, replacing Asp217 with Glu (D217E), results in the creation of a light-driven, single-photon, inward proton transporter. We present the 2.3 Å structure of dark-adapted D217E ASR, which reveals significant changes in the water network surrounding Glu217, as well as a shift in the carbon backbone near retinal-binding Lys210, illustrating a possible pathway leading to the protonation of Glu217 in the cytoplasmic half-channel, located 15 Å from the Schiff base. Crystallographic evidence for the protonation of nearby Glu36 is also discussed, which was described previously by Fourier transform infrared spectroscopy analysis. Finally, two histidine residues near the extracellular surface and their possible role in proton uptake are discussed.
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Affiliation(s)
- Bamboo Dong
- Department of Molecular Biology and Biochemistry, University of California Irvine, Irvine, California
| | | | - Hartmut Luecke
- Department of Molecular Biology and Biochemistry, University of California Irvine, Irvine, California.
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12
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Grisshammer R. New approaches towards the understanding of integral membrane proteins: A structural perspective on G protein-coupled receptors. Protein Sci 2017; 26:1493-1504. [PMID: 28547763 DOI: 10.1002/pro.3200] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2017] [Revised: 05/12/2017] [Accepted: 05/15/2017] [Indexed: 01/12/2023]
Abstract
Three-dimensional structure determination of integral membrane proteins has advanced in unprecedented detail our understanding of mechanistic events of how ion channels, transporters, receptors, and enzymes function. This exciting progress required a tremendous amount of methods development, as exemplified here with G protein-coupled receptors (GPCRs): Optimizing the production of GPCRs in recombinant hosts; increasing the probability of crystal formation using high-affinity ligands, nanobodies, and minimal G proteins for co-crystallization, thus stabilizing receptors into one conformation; using the T4 lysozyme technology and other fusion partners to promote crystal contacts; advancing crystallization methods including the development of novel detergents, and miniaturization and automation of the lipidic cubic phase crystallization method; the concept of conformational thermostabilization of GPCRs; and developing microfocus X-ray synchrotron technologies to analyze small GPCR crystals. However, despite immense progress to explain how GPCRs function, many receptors pose intractable hurdles to structure determination at this time. Three emerging methods, serial femtosecond crystallography, micro electron diffraction, and single particle electron cryo-microscopy, hold promise to overcome current limitations in structural membrane biology.
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Affiliation(s)
- Reinhard Grisshammer
- Department of Health and Human Services, Membrane Protein Structure Function Unit, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Rockville, Maryland, 20852
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13
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Evaluation of diacylphospholipids as boundary lipids for bacteriorhodopsin from structural and functional aspects. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1858:2106-2115. [DOI: 10.1016/j.bbamem.2016.06.006] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/22/2015] [Revised: 06/08/2016] [Accepted: 06/10/2016] [Indexed: 11/18/2022]
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14
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Abstract
Rhodopsins are light-sensing proteins used in optogenetics. The word "rhodopsin" originates from the Greek words "rhodo" and "opsis," indicating rose and sight, respectively. Although the classical meaning of rhodopsin is the red-colored pigment in our eyes, the modern meaning of rhodopsin encompasses photoactive proteins containing a retinal chromophore in animals and microbes. Animal and microbial rhodopsins possess 11-cis and all-trans retinal, respectively, to capture light in seven transmembrane α-helices, and photoisomerizations into all-trans and 13-cis forms, respectively, initiate each function. Ion-transporting proteins can be found in microbial rhodopsins, such as light-gated channels and light-driven pumps, which are the main tools in optogenetics. Light-driven pumps, such as archaeal H(+) pump bacteriorhodopsin (BR) and Cl(-) pump halorhodopsin (HR), were discovered in the 1970s, and their mechanism has been extensively studied. On the other hand, different kinds of H(+) and Cl(-) pumps have been found in marine bacteria, such as proteorhodopsin (PR) and Fulvimarina pelagi rhodopsin (FR), respectively. In addition, a light-driven Na(+) pump was found, Krokinobacter eikastus rhodopsin 2 (KR2). These light-driven ion-pumping microbial rhodopsins are classified as DTD, TSA, DTE, NTQ, and NDQ rhodopsins for BR, HR, PR, FR, and KR2, respectively. Recent understanding of ion-pumping microbial rhodopsins is reviewed in this paper.
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Affiliation(s)
- Hideki Kandori
- Department of Frontier Materials and OptoBioTechnology Research Center, Nagoya Institute of Technology Nagoya, Japan
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15
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Murata M, Sugiyama S, Matsuoka S, Matsumori N. Bioactive Structure of Membrane Lipids and Natural Products Elucidated by a Chemistry-Based Approach. CHEM REC 2015; 15:675-90. [DOI: 10.1002/tcr.201402097] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2014] [Indexed: 12/13/2022]
Affiliation(s)
- Michio Murata
- JST ERATO; Lipid Active Structure Project; Machikaneyama, Toyonaka Osaka 560-0043 Japan
- Department of Chemistry, Graduate School of Science; Osaka University; Machikaneyama, Toyonaka Osaka 563-0043 Japan
| | - Shigeru Sugiyama
- JST ERATO; Lipid Active Structure Project; Machikaneyama, Toyonaka Osaka 560-0043 Japan
- Department of Chemistry, Graduate School of Science; Osaka University; Machikaneyama, Toyonaka Osaka 563-0043 Japan
| | - Shigeru Matsuoka
- JST ERATO; Lipid Active Structure Project; Machikaneyama, Toyonaka Osaka 560-0043 Japan
- Department of Chemistry, Graduate School of Science; Osaka University; Machikaneyama, Toyonaka Osaka 563-0043 Japan
| | - Nobuaki Matsumori
- Department of Chemistry, Graduate School of Science; Osaka University; Machikaneyama, Toyonaka Osaka 563-0043 Japan
- Department of Chemistry, Faculty and Graduate School of Sciences; Kyushu University; 744 Motooka, Nishi-ku Fukuoka 819-0395 Japan
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16
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Schreiner M, Schlesinger R, Heberle J, Niemann HH. Structure of Halorhodopsin from Halobacterium salinarum in a new crystal form that imposes little restraint on the E-F loop. J Struct Biol 2015; 190:373-8. [PMID: 25916754 DOI: 10.1016/j.jsb.2015.04.010] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2015] [Accepted: 04/13/2015] [Indexed: 10/23/2022]
Abstract
Halorhodopsin from the halophilic archaeon Halobacterium salinarum is a membrane located light-driven chloride pump. Upon illumination Halorhodopsin undergoes a reversible photocycle initiated by the all-trans to 13-cis isomerization of the covalently bound retinal chromophore. The photocycle consists of several spectroscopically distinct intermediates. The structural basis of the chloride transport mechanism remains elusive, presumably because packing contacts have so far precluded protein conformational changes in the available crystals. With the intention to structurally characterize late photocycle intermediates by X-ray crystallography we crystallized Halorhodopsin in a new crystal form using the vesicle fusion method. In the new crystal form lateral contacts are mediated by helices A and G. Helices E and F that were suggested to perform large movements during the photocycle are almost unrestrained by packing contacts. This feature might permit the displacement of these helices without disrupting the crystal lattice. Therefore, this new crystal form might be an excellent system for the structural characterization of late Halorhodopsin photocycle intermediates by trapping or by time resolved experiments, especially at XFELs.
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Affiliation(s)
- Madeleine Schreiner
- Department of Chemistry, Bielefeld University, Universitätsstraße 25, 33615 Bielefeld, Germany
| | - Ramona Schlesinger
- Genetic Biophysics, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
| | - Joachim Heberle
- Experimental Molecular Biophysics, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
| | - Hartmut H Niemann
- Department of Chemistry, Bielefeld University, Universitätsstraße 25, 33615 Bielefeld, Germany.
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17
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Abstract
X-ray crystallography remains the most robust method to determine protein structure at the atomic level. However, the bottlenecks of protein expression and purification often discourage further study. In this chapter, we address the most common problems encountered at these stages. Based on our experiences in expressing and purifying antimicrobial efflux proteins, we explain how a pure and homogenous protein sample can be successfully crystallized by the vapor diffusion method. We present our current protocols and methodologies for this technique. Case studies show step-by-step how we have overcome problems related to expression and diffraction, eventually producing high-quality membrane protein crystals for structural determinations. It is our hope that a rational approach can be made of the often anecdotal process of membrane protein crystallization.
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18
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Hong H. Role of Lipids in Folding, Misfolding and Function of Integral Membrane Proteins. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2015; 855:1-31. [DOI: 10.1007/978-3-319-17344-3_1] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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19
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Shevchenko V, Gushchin I, Polovinkin V, Round E, Borshchevskiy V, Utrobin P, Popov A, Balandin T, Büldt G, Gordeliy V. Crystal structure of Escherichia coli-expressed Haloarcula marismortui bacteriorhodopsin I in the trimeric form. PLoS One 2014; 9:e112873. [PMID: 25479443 PMCID: PMC4257550 DOI: 10.1371/journal.pone.0112873] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2014] [Accepted: 10/17/2014] [Indexed: 12/02/2022] Open
Abstract
Bacteriorhodopsins are a large family of seven-helical transmembrane proteins that function as light-driven proton pumps. Here, we present the crystal structure of a new member of the family, Haloarcula marismortui bacteriorhodopsin I (HmBRI) D94N mutant, at the resolution of 2.5 Å. While the HmBRI retinal-binding pocket and proton donor site are similar to those of other archaeal proton pumps, its proton release region is extended and contains additional water molecules. The protein's fold is reinforced by three novel inter-helical hydrogen bonds, two of which result from double substitutions relative to Halobacterium salinarum bacteriorhodopsin and other similar proteins. Despite the expression in Escherichia coli and consequent absence of native lipids, the protein assembles as a trimer in crystals. The unique extended loop between the helices D and E of HmBRI makes contacts with the adjacent protomer and appears to stabilize the interface. Many lipidic hydrophobic tail groups are discernible in the membrane region, and their positions are similar to those of archaeal isoprenoid lipids in the crystals of other proton pumps, isolated from native or native-like sources. All these features might explain the HmBRI properties and establish the protein as a novel model for the microbial rhodopsin proton pumping studies.
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Affiliation(s)
- Vitaly Shevchenko
- Institute of Complex Systems (ICS-6) Structural Biochemistry, Research Centre Jülich GmbH, Jülich, Germany
- Laboratory for advanced studies of membrane proteins, Moscow institute of physics and technology, Dolgoprudniy, Russia
| | - Ivan Gushchin
- Laboratory for advanced studies of membrane proteins, Moscow institute of physics and technology, Dolgoprudniy, Russia
- Univ. Grenoble Alpes, IBS, Grenoble, France
- CNRS, IBS, Grenoble, France
- CEA, IBS, Grenoble, France
| | - Vitaly Polovinkin
- Laboratory for advanced studies of membrane proteins, Moscow institute of physics and technology, Dolgoprudniy, Russia
- Univ. Grenoble Alpes, IBS, Grenoble, France
- CNRS, IBS, Grenoble, France
- CEA, IBS, Grenoble, France
| | - Ekaterina Round
- Institute of Complex Systems (ICS-6) Structural Biochemistry, Research Centre Jülich GmbH, Jülich, Germany
| | - Valentin Borshchevskiy
- Institute of Complex Systems (ICS-6) Structural Biochemistry, Research Centre Jülich GmbH, Jülich, Germany
- Laboratory for advanced studies of membrane proteins, Moscow institute of physics and technology, Dolgoprudniy, Russia
| | - Petr Utrobin
- Laboratory for advanced studies of membrane proteins, Moscow institute of physics and technology, Dolgoprudniy, Russia
- Univ. Grenoble Alpes, IBS, Grenoble, France
- CNRS, IBS, Grenoble, France
| | | | - Taras Balandin
- Institute of Complex Systems (ICS-6) Structural Biochemistry, Research Centre Jülich GmbH, Jülich, Germany
| | - Georg Büldt
- Laboratory for advanced studies of membrane proteins, Moscow institute of physics and technology, Dolgoprudniy, Russia
| | - Valentin Gordeliy
- Institute of Complex Systems (ICS-6) Structural Biochemistry, Research Centre Jülich GmbH, Jülich, Germany
- Laboratory for advanced studies of membrane proteins, Moscow institute of physics and technology, Dolgoprudniy, Russia
- Univ. Grenoble Alpes, IBS, Grenoble, France
- CNRS, IBS, Grenoble, France
- CEA, IBS, Grenoble, France
- European Synchrotron Radiation Facility, Grenoble, France
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20
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High-Resolution Structure of a Membrane Protein Transferred from Amphipol to a Lipidic Mesophase. J Membr Biol 2014; 247:997-1004. [DOI: 10.1007/s00232-014-9700-x] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2014] [Accepted: 06/16/2014] [Indexed: 11/25/2022]
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21
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Chan SK, Kitajima-Ihara T, Fujii R, Gotoh T, Murakami M, Ihara K, Kouyama T. Crystal structure of Cruxrhodopsin-3 from Haloarcula vallismortis. PLoS One 2014; 9:e108362. [PMID: 25268964 PMCID: PMC4182453 DOI: 10.1371/journal.pone.0108362] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2014] [Accepted: 08/26/2014] [Indexed: 01/09/2023] Open
Abstract
Cruxrhodopsin-3 (cR3), a retinylidene protein found in the claret membrane of Haloarcula vallismortis, functions as a light-driven proton pump. In this study, the membrane fusion method was applied to crystallize cR3 into a crystal belonging to space group P321. Diffraction data at 2.1 Å resolution show that cR3 forms a trimeric assembly with bacterioruberin bound to the crevice between neighboring subunits. Although the structure of the proton-release pathway is conserved among proton-pumping archaeal rhodopsins, cR3 possesses the following peculiar structural features: 1) The DE loop is long enough to interact with a neighboring subunit, strengthening the trimeric assembly; 2) Three positive charges are distributed at the cytoplasmic end of helix F, affecting the higher order structure of cR3; 3) The cytoplasmic vicinity of retinal is more rigid in cR3 than in bacteriorhodopsin, affecting the early reaction step in the proton-pumping cycle; 4) the cytoplasmic part of helix E is greatly bent, influencing the proton uptake process. Meanwhile, it was observed that the photobleaching of retinal, which scarcely occurred in the membrane state, became significant when the trimeric assembly of cR3 was dissociated into monomers in the presence of an excess amount of detergent. On the basis of these observations, we discuss structural factors affecting the photostabilities of ion-pumping rhodopsins.
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Affiliation(s)
- Siu Kit Chan
- Department of Physics, Graduate School of Science, Nagoya University, Nagoya, Japan
| | | | - Ryudoh Fujii
- Department of Physics, Graduate School of Science, Nagoya University, Nagoya, Japan
| | - Toshiaki Gotoh
- Department of Physics, Graduate School of Science, Nagoya University, Nagoya, Japan
| | - Midori Murakami
- Department of Physics, Graduate School of Science, Nagoya University, Nagoya, Japan
| | - Kunio Ihara
- Center for Gene Research, Nagoya University, Nagoya, Japan
| | - Tsutomu Kouyama
- Department of Physics, Graduate School of Science, Nagoya University, Nagoya, Japan
- RIKEN Harima Institute/SPring-8, Mikazuki, Sayo, Hyogo, Japan
- * E-mail:
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22
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Wickstrand C, Dods R, Royant A, Neutze R. Bacteriorhodopsin: Would the real structural intermediates please stand up? Biochim Biophys Acta Gen Subj 2014; 1850:536-53. [PMID: 24918316 DOI: 10.1016/j.bbagen.2014.05.021] [Citation(s) in RCA: 79] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2014] [Revised: 05/23/2014] [Accepted: 05/29/2014] [Indexed: 11/18/2022]
Abstract
BACKGROUND Bacteriorhodopsin (bR) is the simplest known light driven proton pump and has been heavily studied using structural methods: eighty four X-ray diffraction, six electron diffraction and three NMR structures of bR are deposited within the protein data bank. Twenty one X-ray structures report light induced structural changes and changes induced by mutation, changes in pH, thermal annealing or X-ray induced photo-reduction have also been examined. SCOPE OF REVIEW We argue that light-induced structural changes that are replicated across several studies by independent research groups are those most likely to represent what is happening in reality. We present both internal distance matrix analyses that sort deposited bR structures into hierarchal trees, and difference Fourier analysis of deposited X-ray diffraction data. MAJOR CONCLUSIONS An internal distance matrix analysis separates most wild-type bR structures according to their different crystal forms, indicating how the protein's structure is influenced by crystallization conditions. A similar analysis clusters eleven studies of illuminated bR crystals as one branch of a hierarchal tree with reproducible movements of the extracellular portion of helix C towards helix G, and of the cytoplasmic portion of helix F away from helices A, B and G. All crystallographic data deposited for illuminated crystals show negative difference density on a water molecule (Wat402) that forms H-bonds to the retinal Schiff Base and two aspartate residues (Asp85, Asp212) in the bR resting state. Other recurring difference density features indicated reproducible side-chain, backbone and water molecule displacements. X-ray induced radiation damage also disorders Wat402 but acts via cleaving the head-groups of Asp85 and Asp212. GENERAL SIGNIFICANCE A remarkable level of agreement exists when deposited structures and crystallographic observations are viewed as a whole. From this agreement a unified picture of the structural mechanism of light-induced proton pumping by bR emerges. This article is part of a Special Issue entitled Structural biochemistry and biophysics of membrane proteins.
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Affiliation(s)
- Cecilia Wickstrand
- Department of Chemistry and Molecular Biology, University of Gothenburg, Box 462, SE-40530 Gothenburg, Sweden
| | - Robert Dods
- Department of Chemistry and Molecular Biology, University of Gothenburg, Box 462, SE-40530 Gothenburg, Sweden
| | - Antoine Royant
- Univ. Grenoble Alpes, IBS, F-38044 Grenoble, France; CNRS, IBS, F-38044 Grenoble, France; CEA, IBS, F-38044 Grenoble, France; European Synchrotron Radiation Facility, F-38043 Grenoble, France.
| | - Richard Neutze
- Department of Chemistry and Molecular Biology, University of Gothenburg, Box 462, SE-40530 Gothenburg, Sweden.
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23
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Jiang X, Dias JA, He X. Structural biology of glycoprotein hormones and their receptors: insights to signaling. Mol Cell Endocrinol 2014; 382:424-451. [PMID: 24001578 DOI: 10.1016/j.mce.2013.08.021] [Citation(s) in RCA: 121] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/23/2013] [Revised: 08/20/2013] [Accepted: 08/24/2013] [Indexed: 01/18/2023]
Abstract
This article reviews the progress made in the field of glycoprotein hormones (GPH) and their receptors (GPHR) by several groups of structural biologists including ourselves aiming to gain insight into GPH signaling mechanisms. The GPH family consists of four members, with follicle-stimulating hormone (FSH) being the prototypic member. GPH members belong to the cystine-knot growth factor superfamily, and their receptors (GPHR), possessing unusually large N-terminal ectodomains, belong to the G-protein coupled receptor Family A. GPHR ectodomains can be divided into two subdomains: a high-affinity hormone binding subdomain primarily centered on the N-terminus, and a second subdomain that is located on the C-terminal region of the ectodomain that is involved in signal specificity. The two subdomains unexpectedly form an integral structure comprised of leucine-rich repeats (LRRs). Following the structure determination of hCG in 1994, the field of FSH structural biology has progressively advanced. Initially, the FSH structure was determined in partially glycosylated free form in 2001, followed by a structure of FSH bound to a truncated FSHR ectodomain in 2005, and the structure of FSH bound to the entire ectodomain in 2012. Comparisons of the structures in three forms led a proposal of a two-step monomeric receptor activation mechanism. First, binding of FSH to the FSHR high-affinity hormone-binding subdomain induces a conformational change in the hormone to form a binding pocket that is specific for a sulfated-tyrosine found as sTyr 335 in FSHR. Subsequently, the sTyr is drawn into the newly formed binding pocket, producing a lever effect on a helical pivot whereby the docking sTyr provides as the 'pull & lift' force. The pivot helix is flanked by rigid LRRs and locked by two disulfide bonds on both sides: the hormone-binding subdomain on one side and the last short loop before the first transmembrane helix on the other side. The lift of the sTyr loop frees the tethered extracellular loops of the 7TM domain, thereby releasing a putative inhibitory influence of the ectodomain, ultimately leading to the activating conformation of the 7TM domain. Moreover, the data lead us to propose that FSHR exists as a trimer and to present an FSHR activation mechanism consistent with the observed trimeric crystal form. A trimeric receptor provides resolution of the enigmatic, but important, biological roles played by GPH residues that are removed from the primary FSH-binding site, as well as several important GPCR phenomena, including negative cooperativity and asymmetric activation. Further reflection pursuant to this review process revealed additional novel structural characteristics such as the identification of a 'seat' sequence in GPH. Together with the 'seatbelt', the 'seat' enables a common heteodimeric mode of association of the common α subunit non-covalently and non-specifically with each of the three different β subunits. Moreover, it was possible to establish a dimensional order that can be used to estimate LRR curvatures. A potential binding pocket for small molecular allosteric modulators in the FSHR 7TM domain has also been identified.
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Affiliation(s)
- Xuliang Jiang
- EMD Serono Research & Development Institute, Billerica, MA 01821, United States.
| | - James A Dias
- Department of Biomedical Sciences, School of Public Health, University at Albany-SUNY, Albany, NY 12222, United States
| | - Xiaolin He
- Department of Molecular Pharmacology and Biological Chemistry, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, United States
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24
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Abstract
We demonstrate that membrane proteins and phospholipids can self-assemble into polyhedral arrangements suitable for structural analysis. Using the Escherichia coli mechanosensitive channel of small conductance (MscS) as a model protein, we prepared membrane protein polyhedral nanoparticles (MPPNs) with uniform radii of ∼ 20 nm. Electron cryotomographic analysis established that these MPPNs contain 24 MscS heptamers related by octahedral symmetry. Subsequent single-particle electron cryomicroscopy yielded a reconstruction at ∼ 1-nm resolution, revealing a conformation closely resembling the nonconducting state. The generality of this approach has been addressed by the successful preparation of MPPNs for two unrelated proteins, the mechanosensitive channel of large conductance and the connexon Cx26, using a recently devised microfluidics-based free interface diffusion system. MPPNs provide not only a starting point for the structural analysis of membrane proteins in a phospholipid environment, but their closed surfaces should facilitate studies in the presence of physiological transmembrane gradients, in addition to potential applications as drug delivery carriers or as templates for inorganic nanoparticle formation.
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25
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Lazarova T, Mlynarczyk K, Filipek S, Kolinski M, Wassenaar TA, Querol E, Renugopalakrishnan V, Viswanathan S, Padrós E. The effect of triple glutamic mutations E9Q/E194Q/E204Q on the structural stability of bacteriorhodopsin. FEBS J 2013; 281:1181-95. [PMID: 24341610 DOI: 10.1111/febs.12694] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2013] [Revised: 11/21/2013] [Accepted: 12/12/2013] [Indexed: 10/25/2022]
Abstract
In the present study, we report on the structural features of the bacteriorhodopsin triple mutant E9Q/E194Q/E204Q (3Glu) of bacteriorhodopsin by combining experimental and molecular dynamics (MD) approaches. In 3Glu mutant, Glu9, Glu194 and Glu204 residues located at the extracellular side of the protein were mutated altogether to glutamines. UV-visible and differential scanning calorimetry experiments served as diagnostic tools for monitoring the resistance against thermal stress of the active site and the tertiary structures of the 3Glu. The analyses of the UV-visible thermal difference spectra demonstrate that the spectral forms at room temperature and the thermal unfolding path differ in the wild-type bacteriorhodopsin and the 3Glu. Even with these spectral differences, the thermal unfolding of the active site occurs at rather similar melting temperatures in both proteins. A noteworthy consequence of the mutations is the altered two-dimensional packing revealed by the lack of the pre-transition peak in differential scanning calorimetry traces of 3Glu mutant, as previously detected in wild-type and the corresponding single mutants. The infrared spectroscopy data agree with the loss of paracrystalinity, illustrating a substantial conversion of αII to αI helical conformation in the 3Glu mutant. Molecular dynamics simulations show higher dynamics flexibility of most of the extracellular regions of 3Glu, which may account for the somewhat lower tertiary structural stability of the mutated protein. Finally, hydrogen bond analysis reveals that the mutated Glu194 and Glu204 residues create ~ 50% less hydrogen bonds with water molecules compared to wild-type bacteriorhodopsin. These results exemplify the role of the water hydrogen-bonding network for structural integrity and conformational flexibility of bacteriorhodopsin.
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Affiliation(s)
- Tzvetana Lazarova
- Unitat de Biofísica, Departament de Bioquímica i de Biologia Molecular, Facultat de Medicina, Universitat Autònoma de Barcelona, Spain; Centre d'Estudis en Biofísica, Universitat Autònoma de Barcelona, Spain
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26
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Zhang J, Mizuno K, Murata Y, Koide H, Murakami M, Ihara K, Kouyama T. Crystal structure of deltarhodopsin-3 from Haloterrigena thermotolerans. Proteins 2013; 81:1585-92. [DOI: 10.1002/prot.24316] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2012] [Revised: 03/25/2013] [Accepted: 04/03/2013] [Indexed: 11/06/2022]
Affiliation(s)
- Jin Zhang
- Department of Physics; Graduate School of Science; Nagoya University; Nagoya Japan
| | - Katsuhide Mizuno
- Department of Physics; Graduate School of Science; Nagoya University; Nagoya Japan
| | - Yuki Murata
- Department of Physics; Graduate School of Science; Nagoya University; Nagoya Japan
| | - Hideaki Koide
- Department of Physics; Graduate School of Science; Nagoya University; Nagoya Japan
| | - Midori Murakami
- Department of Physics; Graduate School of Science; Nagoya University; Nagoya Japan
| | - Kunio Ihara
- Center for Gene Research; Nagoya University; Nagoya Japan
| | - Tsutomu Kouyama
- Department of Physics; Graduate School of Science; Nagoya University; Nagoya Japan
- RIKEN Harima Institute/SPring-8, 1-1-1; Kouto Mikazuki, Sayo, Hyogo Japan
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27
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Caffrey M, Li D, Dukkipati A. Membrane protein structure determination using crystallography and lipidic mesophases: recent advances and successes. Biochemistry 2012; 51:6266-88. [PMID: 22783824 DOI: 10.1021/bi300010w] [Citation(s) in RCA: 81] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
The crystal structure of the β(2)-adrenergic receptor in complex with an agonist and its cognate G protein has just recently been determined. It is now possible to explore in molecular detail the means by which this paradigmatic transmembrane receptor binds agonist, communicates the impulse or signaling event across the membrane, and sets in motion a series of G protein-directed intracellular responses. The structure was determined using crystals of the ternary complex grown in a rationally designed lipidic mesophase by the so-called in meso method. The method is proving to be particularly useful in the G protein-coupled receptor field where the structures of 13 distinct receptor types have been determined in the past 5 years. In addition to receptors, the method has proven to be useful with a wide variety of integral membrane protein classes that include bacterial and eukaryotic rhodopsins, light-harvesting complex II (LHII), photosynthetic reaction centers, cytochrome oxidases, β-barrels, an exchanger, and an integral membrane peptide. This attests to the versatility and range of the method and supports the view that the in meso method should be included in the arsenal of the serious membrane structural biologist. For this to happen, however, the reluctance to adopt it attributable, in part, to the anticipated difficulties associated with handling the sticky, viscous cubic mesophase in which crystals grow must be overcome. Harvesting and collecting diffraction data with the mesophase-grown crystals are also viewed with some trepidation. It is acknowledged that there are challenges associated with the method. Over the years, we have endeavored to establish how the method works at a molecular level and to make it user-friendly. To these ends, tools for handling the mesophase in the pico- to nanoliter volume range have been developed for highly efficient crystallization screening in manual and robotic modes. Methods have been implemented for evaluating the functional activity of membrane proteins reconstituted into the bilayer of the cubic phase as a prelude to crystallogenesis. Glass crystallization plates that provide unparalleled optical quality and sensitivity to nascent crystals have been built. Lipid and precipitant screens have been designed for a more rational approach to crystallogenesis such that the method can now be applied to an even wider variety of membrane protein types. In this work, these assorted advances are outlined along with a summary of the membrane proteins that have yielded to the method. The prospects for and the challenges that must be overcome to further develop the method are described.
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Affiliation(s)
- Martin Caffrey
- Membrane Structural and Functional Biology Group, School of Medicine and School of Biochemistry and Immunology, Trinity College Dublin, Dublin, Ireland.
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28
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Bolla JR, Su CC, Yu EW. Biomolecular membrane protein crystallization. PHILOSOPHICAL MAGAZINE (ABINGDON, ENGLAND) 2012; 92:2648-2661. [PMID: 23869195 PMCID: PMC3712538 DOI: 10.1080/14786435.2012.670734] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Integral membrane proteins comprise approximately 30% of the sequenced genomes, and there is an immediate need for their high-resolution structural information. Currently, the most reliable approach to obtain these structures is x-ray crystallography. However, obtaining crystals of membrane proteins that diffract to high resolution appears to be quite challenging, and remains a major obstacle in structural determination. This brief review summarizes a variety of methodologies for use in crystallizing these membrane proteins. Hopefully, by introducing the available methods, techniques, and providing a general understanding of membrane proteins, a rational decision can be made about now to crystallize these complex materials.
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Affiliation(s)
- Jani Reddy Bolla
- Department of Chemistry, Iowa State University, Ames, IA 50011, USA
| | - Chih-Chia Su
- Department of Chemistry, Iowa State University, Ames, IA 50011, USA
| | - Edward W. Yu
- Department of Chemistry, Iowa State University, Ames, IA 50011, USA
- Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA
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29
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Zhang J, Yamazaki Y, Hikake M, Murakami M, Ihara K, Kouyama T. Crystal structure of the O intermediate of the Leu93→Ala mutant of bacteriorhodopsin. Proteins 2012; 80:2384-96. [DOI: 10.1002/prot.24124] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2012] [Revised: 05/05/2012] [Accepted: 05/14/2012] [Indexed: 12/23/2022]
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30
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Kimble-Hill AC. A review of factors affecting the success of membrane protein crystallization using bicelles. ACTA ACUST UNITED AC 2012. [DOI: 10.1007/s11515-012-1208-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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31
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HU YT, ZHANG CY, MA XL, YIN DC. Progresses on Crystallization Methodology of Membrane Proteins*. PROG BIOCHEM BIOPHYS 2012. [DOI: 10.3724/sp.j.1206.2011.00235] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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32
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Pescitelli G, Woody RW. The Exciton Origin of the Visible Circular Dichroism Spectrum of Bacteriorhodopsin. J Phys Chem B 2012; 116:6751-63. [DOI: 10.1021/jp212166k] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Gennaro Pescitelli
- Dipartimento
di Chimica e Chimica
Industriale, Università degli Studi di Pisa, via Risorgimento 35, I-56126 Pisa, Italy
| | - Robert W. Woody
- Department of Biochemistry and
Molecular Biology, Colorado State University, Fort Collins, Colorado 80523, United States
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Cherezov V. Lipidic cubic phase technologies for membrane protein structural studies. Curr Opin Struct Biol 2011; 21:559-66. [PMID: 21775127 DOI: 10.1016/j.sbi.2011.06.007] [Citation(s) in RCA: 154] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2011] [Revised: 06/06/2011] [Accepted: 06/21/2011] [Indexed: 10/18/2022]
Abstract
Lipidic cubic phase (LCP) is a membrane-mimetic matrix suitable for stabilization and crystallization of membrane proteins in lipidic environment. LCP technologies, however, have not been fully embraced by the membrane protein structural biology community, primarily because of the difficulties associated with handling viscous materials. Recent developments of pre-crystallization assays and improvements in crystal imaging, successes in obtaining high resolution structures of G protein-coupled receptors (GPCRs), and commercial availability of LCP tools and instruments are beginning to attract structural biologists to integrate LCP technologies in their research. This wider acceptance should translate to an increased number of otherwise difficult-to-crystallize membrane protein structures, shedding light on their functional mechanisms and on structural details of lipid-protein interactions.
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Affiliation(s)
- Vadim Cherezov
- Department of Molecular Biology, The Scripps Research Institute, La Jolla, CA 92037, USA.
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Crystallography of membrane proteins: from crystallization to structure. Methods Mol Biol 2010. [PMID: 20665262 DOI: 10.1007/978-1-60761-762-4_5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
Abstract
Although crystallographic studies of membrane proteins have progressed in the last 5 years, the field still remains challenging with several severe bottlenecks. The chapter focuses on the crystallization and describes two approaches, the classical vapor diffusion method and the more recent use of lipidic phases. General aspects on the crystallization principles as well as more practical details are given. In a more synthetic way, the chapter also addresses how structures are solved by X-ray crystallography, and highlights aspects that are specific to membrane proteins.
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Kouyama T, Kanada S, Takeguchi Y, Narusawa A, Murakami M, Ihara K. Crystal Structure of the Light-Driven Chloride Pump Halorhodopsin from Natronomonas pharaonis. J Mol Biol 2010; 396:564-79. [DOI: 10.1016/j.jmb.2009.11.061] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2009] [Revised: 11/21/2009] [Accepted: 11/24/2009] [Indexed: 10/20/2022]
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36
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In Cubo Crystallization of Membrane Proteins. ACTA ACUST UNITED AC 2010. [DOI: 10.1016/b978-0-12-381266-7.00009-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/08/2023]
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Borshchevskiy V, Efremov R, Moiseeva E, Büldt G, Gordeliy V. Overcoming merohedral twinning in crystals of bacteriorhodopsin grown in lipidic mesophase. ACTA CRYSTALLOGRAPHICA SECTION D: BIOLOGICAL CRYSTALLOGRAPHY 2009; 66:26-32. [PMID: 20057046 DOI: 10.1107/s0907444909042838] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/24/2009] [Accepted: 10/18/2009] [Indexed: 11/11/2022]
Abstract
Twinning is one of the most common crystal-growth defects in protein crystallography. There are neither efficient rational approaches for the growth of nontwinned protein crystals nor are there examples of systematic studies of the dependence of the twinning-ratio distribution on crystallization conditions. The description of the twinning phenomenon has been covered even less for membrane-protein crystals and is non-existent for crystals grown using lipidic phases (in meso). In the present work, possibilities for overcoming merohedral twinning are investigated for crystals of the membrane protein bacteriorhodopsin (bR) grown in meso. It is shown that traditional crystallization additives are not effective in the case of the in meso crystallization of bR. The twinning ratio was determined for 310 crystals grown under different crystallization conditions. A correlation of the twinning ratio with the growth rate of the crystals was observed. Slow growth indicated that crystals had a noticeable chance of avoiding twinning. Model calculations were performed in order to rationalize this observation. The calculations confirmed the experimental observation that most crystals consist of two twin domains and showed that under this condition small changes in the probability of twin-domain formation lead to dramatic changes in the number of nontwinned crystals, which explains why slow crystal growth results in a considerable number of nontwinned crystals.
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Affiliation(s)
- Valentin Borshchevskiy
- Laboratoire des Protéines Membranaires, Institute de Biologie Structurale J.-P. Ebel, UMR5075 CEA-CNRS-UJF, Grenoble 38027, France
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38
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Yamamoto M, Hayakawa N, Murakami M, Kouyama T. Crystal structures of different substrates of bacteriorhodopsin's M intermediate at various pH levels. J Mol Biol 2009; 393:559-73. [PMID: 19712684 DOI: 10.1016/j.jmb.2009.08.047] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2009] [Revised: 08/18/2009] [Accepted: 08/19/2009] [Indexed: 11/16/2022]
Abstract
The hexagonal P622 crystal of bacteriorhodopsin, which is made up of stacked membranes, is stable provided that the precipitant concentration in the soaking solution is higher than a critical value (i.e., 1.5 M ammonium sulfate). Diffraction data showed that the crystal lattice shrank linearly with increasing precipitant concentration, due primarily to narrowing of intermembrane spaces. Although the crystal shrinkage did not affect the rate of formation of the photoreaction M intermediate, its lifetime increased exponentially with the precipitant concentration. It was suggested that the energetic barrier of the M-to-N transition becomes higher when the motional freedom of the EF loop is reduced by crystal lattice force. As a result of this property, the M state accumulated predominantly when the crystal that was soaked at a high precipitant concentration was illuminated at room temperature. Structural data obtained at various pH levels showed that the overall structure of M is not strongly dependent on pH, except that Glu194 and Glu204 in the proton release complex are more separated at pH 7 than at pH 4.4. This result suggests that light-induced disruption of the paired structure of Glu194 and Glu204 is incomplete when external pH is lower than the pK(a) value of the proton release group in the M state.
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Affiliation(s)
- Masataka Yamamoto
- Department of Physics, Graduate School of Science, Nagoya University, Nagoya, Japan
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Abstract
A detailed protocol for crystallizing membrane proteins that makes use of lipidic mesophases is described. This has variously been referred to as the lipid cubic phase or in meso method. The method has been shown to be quite general in that it has been used to solve X-ray crystallographic structures of prokaryotic and eukaryotic proteins, proteins that are monomeric, homo- and hetero-multimeric, chromophore-containing and chromophore-free, and alpha-helical and beta-barrel proteins. Its most recent successes are the human-engineered beta(2)-adrenergic and adenosine A(2A) G protein-coupled receptors. Protocols are provided for preparing and characterizing the lipidic mesophase, for reconstituting the protein into the monoolein-based mesophase, for functional assay of the protein in the mesophase and for setting up crystallizations in manual mode. Methods for harvesting microcrystals are also described. The time required to prepare the protein-loaded mesophase and to set up a crystallization plate manually is about 1 h.
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Affiliation(s)
- Martin Caffrey
- Membrane Structural and Functional Biology Group, University of Limerick, Limerick, Ireland.
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40
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Wassenaar TA, Daura X, Padrós E, Mark AE. Calcium binding to the purple membrane: A molecular dynamics study. Proteins 2009; 74:669-81. [PMID: 18704943 DOI: 10.1002/prot.22182] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The purple membrane (PM) is a specialized membrane patch found in halophilic archaea, containing the photoreceptor bacteriorhodopsin (bR). It is long known that calcium ions bind to the PM, but their position and role remain elusive to date. Molecular dynamics simulations in conjunction with a highly detailed model of the PM have been used to investigate the stability of calcium ions placed at three proposed cation binding sites within bR, one near the Schiff base, one in the region of the proton release group, and one near Glu9. The simulations suggest that, of the sites investigated, the binding of calcium ions was most likely at the proton release group. Binding in the region of the Schiff base, while possible, was associated with significant changes in local geometry. Calcium ions placed near Glu9 in the interior of bR (simultaneously to a Ca(2+) near the Schiff base and another one near the Glu194-Glu204 site) were not stable. The results obtained are discussed in relation to recent experimental observations and theoretical considerations.
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Affiliation(s)
- Tsjerk A Wassenaar
- Department of Biophysical Chemistry, Groningen Biomolecular Sciences and Biotechnology Institute (GBB), University of Groningen, 9747 AG Groningen, The Netherlands
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Ron I, Friedman N, Cahen D, Sheves M. Selective electroless deposition of metal clusters on solid-supported bacteriorhodopsin: applications to orientation labeling and electrical contacts. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2008; 4:2271-2278. [PMID: 19016493 DOI: 10.1002/smll.200800524] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Controlling the orientation of bacteriorhodopsin (bR) monolayers is an important step in studying and utilizing such membranes in a solid-state configuration in, for example, photoelectric applications. Macroscopic monolayers of bR have been fabricated in a variety of ways, but characterization of the distribution of the two possible orientations in which the membrane fragments can adsorb has not yet been addressed experimentally. Here, an approach is presented that labels only one of the membrane surfaces by electroless growth of metal nanoparticles on top of the solid-supported membranes. In this way, it is possible to observe which surface of the membranes is actually adsorbed to the substrate. How this technique serves to interface the membranes with a top metal contact for further electrical measurements is also demonstrated.
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Affiliation(s)
- Izhar Ron
- Department of Materials and Interfaces, Weizmann Institute of Science, P. O. Box 26, Rehovot 76100, Israel
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42
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Hayakawa N, Kasahara T, Hasegawa D, Yoshimura K, Murakami M, Kouyama T. Effect of Xenon Binding to a Hydrophobic Cavity on the Proton Pumping Cycle in Bacteriorhodopsin. J Mol Biol 2008; 384:812-23. [PMID: 18930734 DOI: 10.1016/j.jmb.2008.09.075] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2008] [Revised: 09/21/2008] [Accepted: 09/25/2008] [Indexed: 11/25/2022]
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43
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Yoshimura K, Kouyama T. Structural Role of Bacterioruberin in the Trimeric Structure of Archaerhodopsin-2. J Mol Biol 2008; 375:1267-81. [DOI: 10.1016/j.jmb.2007.11.039] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2007] [Revised: 11/08/2007] [Accepted: 11/14/2007] [Indexed: 02/05/2023]
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44
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Balashov SP, Ebrey TG. Trapping and Spectroscopic Identification of the Photointermediates of Bacteriorhodopsin at Low Temperatures¶. Photochem Photobiol 2007. [DOI: 10.1562/0031-8655(2001)0730453tasiot2.0.co2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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45
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Paiva ACM, Oliveira L, Horn F, Bywater RP, Vriend G. Modeling GPCRs. ERNST SCHERING FOUNDATION SYMPOSIUM PROCEEDINGS 2007:23-47. [PMID: 17703576 DOI: 10.1007/2789_2006_002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Many GPCR models have been built over the years for many different purposes, of which drug-design undoubtedly has been the most frequent one. The release of the structure of bovine rhodopsin in August 2000 enabled us to analyze models built before that period to learn things for the models we build today. We conclude that the GPCR modeling field is riddled with "common knowledge". Several characteristics of the bovine rhodopsin structure came as a big surprise, and had obviously not been predicted, which led to large errors in the models. Some of these surprises, however, could have been predicted if the modelers had more rigidly stuck to the rule that holds for all models, namely that a model should explain all experimental facts, and not just those facts that agree with the modeler's preconceptions.
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Affiliation(s)
- A C M Paiva
- CMBI NCMLS, UMC, Geert Grooteplein 28, 6525 GA Nijmegen, The Netherlands
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46
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Martinelli A, Tuccinardi T. An overview of recent developments in GPCR modelling: methods and validation. Expert Opin Drug Discov 2006; 1:459-76. [DOI: 10.1517/17460441.1.5.459] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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47
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Efremov R, Gordeliy VI, Heberle J, Büldt G. Time-resolved microspectroscopy on a single crystal of bacteriorhodopsin reveals lattice-induced differences in the photocycle kinetics. Biophys J 2006; 91:1441-51. [PMID: 16731567 PMCID: PMC1518640 DOI: 10.1529/biophysj.106.083345] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The determination of the intermediate state structures of the bacteriorhodopsin photocycle has lead to an unprecedented level of understanding of the catalytic process exerted by a membrane protein. However, the crystallographic structures of the intermediate states are only relevant if the working cycle is not impaired by the crystal lattice. Therefore, we applied visible and Fourier transform infrared spectroscopy (FTIR) microspectroscopy with microsecond time resolution to compare the photoreaction of a single bacteriorhodopsin crystal to that of bacteriorhodopsin residing in the native purple membrane. The analysis of the FTIR difference spectra of the resolved intermediate states reveals great similarity in structural changes taking place in the crystal and in PM. However, the kinetics of the photocycle are significantly altered in the three-dimensional crystal as compared to PM. Strikingly, the L state decay is accelerated in the crystal, whereas the M decay is delayed. The physical origin of this deviation and the implications for trapping of intermediate states are discussed. As a methodological advance, time-resolved step-scan FTIR spectroscopy on a single protein crystal is demonstrated for the first time which may be used in the future to gauge the functionality of other crystallized proteins with the molecular resolution of vibrational spectroscopy.
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Affiliation(s)
- R Efremov
- Forschungszentrum Jülich, IBI-2: Structural Biology, 52425 Jülich, Germany
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48
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Enami N, Yoshimura K, Murakami M, Okumura H, Ihara K, Kouyama T. Crystal structures of archaerhodopsin-1 and -2: Common structural motif in archaeal light-driven proton pumps. J Mol Biol 2006; 358:675-85. [PMID: 16540121 DOI: 10.1016/j.jmb.2006.02.032] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2005] [Revised: 02/09/2006] [Accepted: 02/14/2006] [Indexed: 10/24/2022]
Abstract
Archaerhodopsin-1 and -2 (aR-1 and aR-2) are light-driven proton pumps found in Halorubrum sp. aus-1 and -2, which share 55-58% sequence identity with bacteriorhodopsin (bR), a proton pump found in Halobacterium salinarum. In this study, aR-1 and aR-2 were crystallized into 3D crystals belonging to P4(3)2(1)2 (a = b = 128.1 A, c = 117.6 A) and C222(1) (a = 122.9 A, b = 139.5 A, c = 108.1 A), respectively. In both the crystals, the asymmetric unit contains two protein molecules with slightly different conformations. Each subunit is composed of seven helical segments as seen in bR but, unlike bR, aR-1 as well as aR-2 has a unique omega loop near the N terminus. It is found that the proton pathway in the extracellular half (i.e. the proton release channel) is more opened in aR-2 than in aR-1 or bR. This structural difference accounts for a large variation in the pKa of the acid purple-to-blue transition among the three proton pumps. All the aromatic residues surrounding the retinal polyene chain are conserved among the three proton pumps, confirming a previous argument that these residues are required for the stereo-specificity of the retinal isomerization. In the cytoplasmic half, the region surrounded by helices B, C and G is highly conserved, while the structural conservation is very low for residues extruded from helices E and F. Structural conservation of the hydrophobic residues located on the proton uptake pathway suggests that their precise arrangement is necessary to prevent a backward flow of proton in the presence of a large pH gradient and membrane potential. An empty cavity is commonly seen in the vicinity of Leu93 contacting the retinal C13 methyl. Existence of such a cavity is required to allow a large rotation of the side-chain of Leu93 at the early stage of the photocycle, which has been shown to accompany water translocation across the Schiff base.
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Affiliation(s)
- Nobuo Enami
- Department of Physics, Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan
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49
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Park Y, Helms V. How strongly do sequence conservation patterns and empirical scales correlate with exposure patterns of transmembrane helices of membrane proteins? Biopolymers 2006; 83:389-99. [PMID: 16838301 DOI: 10.1002/bip.20569] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Given the difficulty in determining high-resolution structures of helical membrane proteins, sequence-based prediction methods can be useful in elucidating diverse physiological processes mediated by this important class of proteins. Predicting the angular orientations of transmembrane (TM) helices about the helix axes, based on the helix parameters from electron microscopy data, is a classical problem in this regard. This problem has triggered the development of a number of different empirical scales. Recently, sequence conservation patterns were also made use of for improved predictions. Empirical scales and sequence conservation patterns (collectively termed as "prediction scales") have also found frequent applications in other research areas of membrane proteins: for example, in structure modeling and in prediction of buried TM helices. This trend is expected to grow in the near future unless there are revolutionary developments in the experimental characterization of membrane proteins. Thus, it is timely and imperative to carry out a comprehensive benchmark test over the prediction scales proposed so far to determine their pros and cons. In the current analysis, we use exposure patterns of TM helices as a golden standard, because if one develops a prediction scale that correlates perfectly with exposure patterns of TM helices, it will enable one to predict buried residues (or buried faces) of TM helices with an accuracy of 100%. Our analysis reveals several important points. (1) It demonstrates that sequence conservation patterns are much more strongly correlated with exposure patterns of TM helices than empirical scales. (2) Scales that were specifically parameterized using structure data (structure-based scales) display stronger correlation than hydrophobicity-based scales, as expected. (3) A nonnegligible difference is observed among the structure-based scales in their correlational property, suggesting that not every learning algorithm is equally effective. (4) A straightforward framework of optimally combining sequence conservation patterns and empirical scales is proposed, which reveals that improvements gained from combining the two sources of information are not dramatic in almost all cases. In turn, this calls for the development of fundamentally different scales that capture the essentials of membrane protein folding for substantial improvements.
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Affiliation(s)
- Yungki Park
- Center for Bioinformatics, Saarland University, 66041 Saarbruecken, Germany
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50
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Theisen MJ, Potocky TB, McQuade DT, Gellman SH, Chiu ML. Crystallization of bacteriorhodopsin solubilized by a tripod amphiphile. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2005; 1751:213-6. [PMID: 15963773 DOI: 10.1016/j.bbapap.2005.04.011] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/21/2005] [Revised: 04/22/2005] [Accepted: 04/26/2005] [Indexed: 11/16/2022]
Abstract
Bacteriorhodopsin (bR) is solubilized efficiently as a monomer by a novel surfactant, a tripod amphiphile (TPA), which permits the formation of purple hexagonal bR crystals under several conditions. The crystals, although small, diffract to 2.5 A resolution using synchrotron radiation. TPA may be useful for the solubilization, purification, and crystallization of other membrane proteins.
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Affiliation(s)
- Michael J Theisen
- Department of Structural Biology, Abbott Laboratories, Abbott Park, Illinois 60064-6098, USA
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