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Abstract
Microbial rhodopsins are diverse photoreceptive proteins containing a retinal chromophore and are found in all domains of cellular life and are even encoded in genomes of viruses. These rhodopsins make up two families: type 1 rhodopsins and the recently discovered heliorhodopsins. These families have seven transmembrane helices with similar structures but opposing membrane orientation. Microbial rhodopsins participate in a portfolio of light-driven energy and sensory transduction processes. In this review we present data collected over the last two decades about these rhodopsins and describe their diversity, functions, and biological and ecological roles. Expected final online publication date for the Annual Review of Microbiology, Volume 75 is October 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
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Affiliation(s)
- Andrey Rozenberg
- Faculty of Biology, Technion-Israel Institute of Technology, Haifa 3200003, Israel; ,
| | - Keiichi Inoue
- The Institute for Solid State Physics, The University of Tokyo, Kashiwa 277-8581, Japan;
| | - Hideki Kandori
- Department of Life Science and Applied Chemistry, Nagoya Institute of Technology, Nagoya 466-8555, Japan;
| | - Oded Béjà
- Faculty of Biology, Technion-Israel Institute of Technology, Haifa 3200003, Israel; ,
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Kikuchi M, Kojima K, Nakao S, Yoshizawa S, Kawanishi S, Shibukawa A, Kikukawa T, Sudo Y. Functional expression of the eukaryotic proton pump rhodopsin OmR2 in Escherichia coli and its photochemical characterization. Sci Rep 2021; 11:14765. [PMID: 34285294 PMCID: PMC8292405 DOI: 10.1038/s41598-021-94181-w] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2021] [Accepted: 07/07/2021] [Indexed: 01/05/2023] Open
Abstract
Microbial rhodopsins are photoswitchable seven-transmembrane proteins that are widely distributed in three domains of life, archaea, bacteria and eukarya. Rhodopsins allow the transport of protons outwardly across the membrane and are indispensable for light-energy conversion in microorganisms. Archaeal and bacterial proton pump rhodopsins have been characterized using an Escherichia coli expression system because that enables the rapid production of large amounts of recombinant proteins, whereas no success has been reported for eukaryotic rhodopsins. Here, we report a phylogenetically distinct eukaryotic rhodopsin from the dinoflagellate Oxyrrhis marina (O. marina rhodopsin-2, OmR2) that can be expressed in E. coli cells. E. coli cells harboring the OmR2 gene showed an outward proton-pumping activity, indicating its functional expression. Spectroscopic characterization of the purified OmR2 protein revealed several features as follows: (1) an absorption maximum at 533 nm with all-trans retinal chromophore, (2) the possession of the deprotonated counterion (pKa = 3.0) of the protonated Schiff base and (3) a rapid photocycle through several distinct photointermediates. Those features are similar to those of known eukaryotic proton pump rhodopsins. Our successful characterization of OmR2 expressed in E. coli cells could build a basis for understanding and utilizing eukaryotic rhodopsins.
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Affiliation(s)
- Masuzu Kikuchi
- Division of Pharmaceutical Sciences, Okayama University, Okayama, 700-8530, Japan
| | - Keiichi Kojima
- Division of Pharmaceutical Sciences, Okayama University, Okayama, 700-8530, Japan.,Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, 700-8530, Japan
| | - Shin Nakao
- Division of Pharmaceutical Sciences, Okayama University, Okayama, 700-8530, Japan
| | - Susumu Yoshizawa
- Atmosphere and Ocean Research Institute, The University of Tokyo, Chiba, 277-8564, Japan
| | - Shiho Kawanishi
- Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, 700-8530, Japan
| | - Atsushi Shibukawa
- Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, 700-8530, Japan
| | - Takashi Kikukawa
- Faculty of Advanced Life Science, Hokkaido University, Sapporo, 060-0810, Japan.,Global Station for Soft Matter, GI-CoRE, Hokkaido University, Sapporo, 001-0021, Japan
| | - Yuki Sudo
- Division of Pharmaceutical Sciences, Okayama University, Okayama, 700-8530, Japan. .,Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, 700-8530, Japan.
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Discovery of a microbial rhodopsin that is the most stable in extreme environments. iScience 2021; 24:102620. [PMID: 34151231 PMCID: PMC8188555 DOI: 10.1016/j.isci.2021.102620] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2021] [Revised: 04/28/2021] [Accepted: 05/19/2021] [Indexed: 12/18/2022] Open
Abstract
Microbial rhodopsin is a retinal protein that functions as an ion pump, channel, and sensory transducer, as well as a light sensor, as in biosensors and biochips. Tara76 rhodopsin is a typical proton-pumping rhodopsin that exhibits strong stability against extreme pH, detergent, temperature, salt stress, and dehydration stress and even under dual and triple conditions. Tara76 rhodopsin has a thermal stability approximately 20 times higher than that of thermal rhodopsin at 80°C and is even stable at 85°C. Tara76 rhodopsin is also stable at pH 0.02 to 13 and exhibits strong resistance in detergent, including Triton X-100 and SDS. We tested the current flow that electrical current flow across dried proteins on the paper at high temperatures using an electrode device, which was measured stably from 25°C up to 120°C. These properties suggest that this Tara76 rhodopsin is suitable for many applications in the fields of bioengineering and biotechnology.
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Inoue K. Diversity, Mechanism, and Optogenetic Application of Light-Driven Ion Pump Rhodopsins. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2021; 1293:89-126. [PMID: 33398809 DOI: 10.1007/978-981-15-8763-4_6] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Ion-transporting microbial rhodopsins are widely used as major molecular tools in optogenetics. They are categorized into light-gated ion channels and light-driven ion pumps. While the former passively transport various types of cations and anions in a light-dependent manner, light-driven ion pumps actively transport specific ions, such as H+, Na+, Cl-, against electrophysiological potential by using light energy. Since the ion transport by these pumps induces hyperpolarization of membrane potential and inhibit neural firing, light-driven ion-pumping rhodopsins are mostly applied as inhibitory optogenetics tools. Recent progress in genome and metagenome sequencing identified more than several thousands of ion-pumping rhodopsins from a wide variety of microbes, and functional characterization studies has been revealing many new types of light-driven ion pumps one after another. Since light-gated channels were reviewed in other chapters in this book, here the rapid progress in functional characterization, molecular mechanism study, and optogenetic application of ion-pumping rhodopsins were reviewed.
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Affiliation(s)
- Keiichi Inoue
- The Institute for Solid State Physics, The University of Tokyo, Chiba, Japan.
- PRESTO, Japan Science and Technology Agency, Saitama, Japan.
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