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Hart JE, Gardner KH. Lighting the way: Recent insights into the structure and regulation of phototropin blue light receptors. J Biol Chem 2021; 296:100594. [PMID: 33781746 PMCID: PMC8086140 DOI: 10.1016/j.jbc.2021.100594] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2020] [Revised: 03/24/2021] [Accepted: 03/25/2021] [Indexed: 02/06/2023] Open
Abstract
The phototropins (phots) are light-activated kinases that are critical for plant physiology and the many diverse optogenetic tools that they have inspired. Phototropins combine two blue-light-sensing Light-Oxygen-Voltage (LOV) domains (LOV1 and LOV2) and a C-terminal serine/threonine kinase domain, using the LOV domains to control the catalytic activity of the kinase. While much is known about the structure and photochemistry of the light-perceiving LOV domains, particularly in how activation of the LOV2 domain triggers the unfolding of alpha helices that communicate the light signal to the kinase domain, many questions about phot structure and mechanism remain. Recent studies have made progress addressing these questions by utilizing small-angle X-ray scattering (SAXS) and other biophysical approaches to study multidomain phots from Chlamydomonas and Arabidopsis, leading to models where the domains have an extended linear arrangement, with the regulatory LOV2 domain contacting the kinase domain N-lobe. We discuss this and other advances that have improved structural and mechanistic understanding of phot regulation in this review, along with the challenges that will have to be overcome to obtain high-resolution structural information on these exciting photoreceptors. Such information will be essential to advancing fundamental understanding of plant physiology while enabling engineering efforts at both the whole plant and molecular levels.
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Affiliation(s)
- Jaynee E Hart
- Structural Biology Initiative, CUNY Advanced Science Research Center, New York, New York, USA
| | - Kevin H Gardner
- Structural Biology Initiative, CUNY Advanced Science Research Center, New York, New York, USA; Department of Chemistry and Biochemistry, City College of New York, New York, USA; PhD Programs in Biochemistry, Chemistry, and Biology, Graduate Center, City University of New York, New York, USA.
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2
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Domain Organization in Plant Blue-Light Receptor Phototropin2 of Arabidopsis thaliana Studied by Small-Angle X-ray Scattering. Int J Mol Sci 2020; 21:ijms21186638. [PMID: 32927860 PMCID: PMC7555306 DOI: 10.3390/ijms21186638] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2020] [Revised: 09/06/2020] [Accepted: 09/07/2020] [Indexed: 01/10/2023] Open
Abstract
Phototropin2 (phot2) is a blue-light (BL) receptor protein that regulates the BL-dependent activities of plants for efficient photosynthesis. Phot2 is composed of two light-oxygen-voltage sensing domains (LOV1 and LOV2) to absorb BL, and a kinase domain. Photo-activated LOV domains, especially LOV2, play a major role in photo-dependent increase in the phosphorylation activity of the kinase domain. The atomic details of the overall structure of phot2 and the intramolecular mechanism to convert BL energy to a phosphorylation signal remain unknown. We performed structural studies on the LOV fragments LOV1, LOV2, LOV2-linker, and LOV2-kinase, and full-length phot2, using small-angle X-ray scattering (SAXS). The aim of the study was to understand structural changes under BL irradiation and discuss the molecular mechanism that enhance the phosphorylation activity under BL. SAXS is a suitable technique for visualizing molecular structures of proteins in solution at low resolution and is advantageous for monitoring their structural changes in the presence of external physical and/or chemical stimuli. Structural parameters and molecular models of the recombinant specimens were obtained from SAXS profiles in the dark, under BL irradiation, and after dark reversion. LOV1, LOV2, and LOV2-linker fragments displayed minimal structural changes. However, BL-induced rearrangements of functional domains were noted for LOV2-kinase and full-length phot2. Based on the molecular model together with the absorption measurements and biochemical assays, we discuss the intramolecular interactions and domain motions necessary for BL-enhanced phosphorylation activity of phot2.
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Measurements of Photoreaction and Kinase Activity of Phototropin, a Photoreceptor Protein for Tropic Response in Plants: Involvement of Kinase Activity in the Photosensitivity of Tropic Response. Methods Mol Biol 2019. [PMID: 30694475 DOI: 10.1007/978-1-4939-9015-3_14] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
Abstract
Phototropin is a photoreceptor protein responsible for phototropic responses in plants. A phototropin molecule has two photoreceptive domains named LOV1 and LOV2 in the N-terminal region. Blue light absorbed by a chromophore in these domains triggers conformational changes in the protein moiety. The C-terminal region of phototropin forms a Ser/Thr kinase that is activated by these conformational changes. The activated phototropin kinase transmits signals downstream leading to tropic responses. The lifetime of the activated state may concern the sensitivity of the tropic responses to light. Thus, spectrophotometric and kinase activity analyses of phototropin are important to understand the light signaling processes related to the photosensitivity. The preparation of polypeptide samples of Arabidopsis phototropin and the methods of spectroscopic measurements and kinase assay of these samples are shown in this chapter.
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Oide M, Okajima K, Nakagami H, Kato T, Sekiguchi Y, Oroguchi T, Hikima T, Yamamoto M, Nakasako M. Blue light-excited LOV1 and LOV2 domains cooperatively regulate the kinase activity of full-length phototropin2 from Arabidopsis. J Biol Chem 2017; 293:963-972. [PMID: 29196607 DOI: 10.1074/jbc.ra117.000324] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2017] [Revised: 11/15/2017] [Indexed: 11/06/2022] Open
Abstract
Phototropin2 (phot2) is a blue-light (BL) receptor that regulates BL-dependent activities for efficient photosynthesis in plants. phot2 comprises two BL-receiving light-oxygen-voltage-sensing domains (LOV1 and LOV2) and a kinase domain. BL-excited LOV2 is thought to be primarily responsible for the BL-dependent activation of the kinase. However, the molecular mechanisms by which small BL-induced conformational changes in the LOV2 domain are transmitted to the kinase remain unclear. Here, we used full-length wild-type and mutant phot2 proteins from Arabidopsis to study their molecular properties in the dark and under BL irradiation. Phosphorylation assays and absorption measurements indicated that the LOV1 domain assists the thermal relaxation of BL-excited LOV2 and vice versa. Using small-angle X-ray scattering and electron microscopy, we observed that phot2 forms a dimer and has a rod shape with a maximum length of 188 Å and a radius of gyration of 44 Å. Under BL, phot2 displayed large conformational changes that bent the rod shape. By superimposing the crystal structures of the LOV1 dimer, LOV2, and a homology model of the kinase to the observed changes, we inferred that the BL-dependent change consisted of positional shifts of both LOV2 and the kinase relative to LOV1. Furthermore, phot2 mutants lacking the photocycle in LOV1 or LOV2 still exhibited conformational changes under BL, suggesting that LOV1 and LOV2 cooperatively contribute to the conformational changes that activate the kinase. These results suggest that BL-activated LOV1 contributes to the kinase activity of phot2. We discuss the possible intramolecular interactions and signaling mechanisms in phot2.
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Affiliation(s)
- Mao Oide
- From the Department of Physics, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoko-ku, Yokohama, Kanagawa 223-8522, Japan.,RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan
| | - Koji Okajima
- From the Department of Physics, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoko-ku, Yokohama, Kanagawa 223-8522, Japan, .,RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan
| | - Hirofumi Nakagami
- RIKEN Center for Sustainable Resource Science, Yokohama 230-0045, Japan.,Max Planck Institute for Plant Breeding Research, 50829 Cologne, Germany, and
| | - Takayuki Kato
- Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Yuki Sekiguchi
- From the Department of Physics, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoko-ku, Yokohama, Kanagawa 223-8522, Japan.,RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan
| | - Tomotaka Oroguchi
- From the Department of Physics, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoko-ku, Yokohama, Kanagawa 223-8522, Japan.,RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan
| | - Takaaki Hikima
- RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan
| | - Masaki Yamamoto
- RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan
| | - Masayoshi Nakasako
- From the Department of Physics, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoko-ku, Yokohama, Kanagawa 223-8522, Japan.,RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan
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Takakado A, Nakasone Y, Okajima K, Tokutomi S, Terazima M. Light-Induced Conformational Changes of LOV2-Kinase and the Linker Region in Arabidopsis Phototropin2. J Phys Chem B 2017; 121:4414-4421. [DOI: 10.1021/acs.jpcb.7b01552] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Akira Takakado
- Department
of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
| | - Yusuke Nakasone
- Department
of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
| | - Koji Okajima
- Department
of Biological Science, Graduate School of Science, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan
| | - Satoru Tokutomi
- Department
of Biological Science, Graduate School of Science, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan
| | - Masahide Terazima
- Department
of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
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Oide M, Okajima K, Kashojiya S, Takayama Y, Oroguchi T, Hikima T, Yamamoto M, Nakasako M. Blue Light-excited Light-Oxygen-Voltage-sensing Domain 2 (LOV2) Triggers a Rearrangement of the Kinase Domain to Induce Phosphorylation Activity in Arabidopsis Phototropin1. J Biol Chem 2016; 291:19975-84. [PMID: 27484797 DOI: 10.1074/jbc.m116.735787] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2016] [Indexed: 11/06/2022] Open
Abstract
Phototropin1 is a blue light (BL) receptor in plants and shows BL-dependent kinase activation. The BL-excited light-oxygen-voltage-sensing domain 2 (LOV2) is primarily responsible for the activation of the kinase domain; however, the molecular mechanism by which conformational changes in LOV2 are transmitted to the kinase domain remains unclear. Here, we investigated BL-induced structural changes of a minimum functional fragment of Arabidopsis phototropin1 composed of LOV2, the kinase domain, and a linker connecting the two domains using small-angle x-ray scattering (SAXS). The fragment existed as a dimer and displayed photoreversible SAXS changes reflected in the radii of gyration of 42.9 Å in the dark and 48.8 Å under BL irradiation. In the dark, the molecular shape reconstructed from the SAXS profiles appeared as two bean-shaped lobes in a twisted arrangement that was 170 Å long, 80 Å wide, and 50 Å thick. The molecular shape under BL became slightly elongated from that in the dark. By fitting the crystal structure of the LOV2 dimer and a homology model of the kinase domain to their inferred shapes, the BL-dependent change could be interpreted as the positional shift in the kinase domain relative to that of the LOV2 dimer. In addition, we found that lysine 475, a functionally important residue, in the N-terminal region of LOV2 plays a critical role in transmitting the structural changes in LOV2 to the kinase domain. The interface between the domains is critical for signaling, suitably changing the structure to activate the kinase in response to conformational changes in the adjoining LOV2.
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Affiliation(s)
- Mao Oide
- From the Department of Physics, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, Kanagawa 223-8522, Japan, RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan, and
| | - Koji Okajima
- From the Department of Physics, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, Kanagawa 223-8522, Japan, RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan, and
| | - Sachiko Kashojiya
- RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan, and the Department of Biological Science, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, Japan
| | - Yuki Takayama
- From the Department of Physics, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, Kanagawa 223-8522, Japan, RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan, and
| | - Tomotaka Oroguchi
- From the Department of Physics, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, Kanagawa 223-8522, Japan, RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan, and
| | - Takaaki Hikima
- RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan, and
| | - Masaki Yamamoto
- RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan, and
| | - Masayoshi Nakasako
- From the Department of Physics, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, Kanagawa 223-8522, Japan, RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan, and
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Okajima K. Molecular mechanism of phototropin light signaling. JOURNAL OF PLANT RESEARCH 2016; 129:149-157. [PMID: 26815763 DOI: 10.1007/s10265-016-0783-6] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2015] [Accepted: 12/24/2015] [Indexed: 06/05/2023]
Abstract
Phototropin (phot) is a blue light (BL) receptor kinase involved in the BL responses of several species, ranging from green algae to higher plants. Phot converts BL signals from the environment into biochemical signals that trigger cellular responses. In phot, the LOV1 and LOV2 domains of the N-terminal region utilize BL for cyclic photoreactions and regulate C-terminal serine/threonine kinase (STK) activity. LOV2-STK peptides are the smallest functional unit of phot and are useful for understanding regulation mechanisms. The combined analysis of spectroscopy and STK activity assay in Arabidopsis phots suggests that the decay speed of the photo-intermediate S390 in LOV2 is one of the factors contributing to light sensitive kinase activity. LOV2 and STK are thought to be adjacent to each other in LOV2-STK with small angle scattering (SAXS). BL irradiation induces LOV2-STK elongation, resulting in LOV2 shifting away from STK. The N- and C-terminal lateral regions of LOV2, A'α-helix, Jα-helix, and A'α/Aβ gap are responsible for the propagation of the BL signal to STK via conformational changes. The comparison between LOV2-STK and full-length phot from Chlamydomonas suggests that LOV1 is directly adjacent to LOV2 in LOV2-STK; therefore, LOV1 may indirectly regulate STK. The molecular mechanism of phot is discussed.
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Affiliation(s)
- Koji Okajima
- Department of Physics, Keio University, 3-14-1, Hiyoshi, Kouhoku-ku, Yokohama, Kanagawa, 223-8522, Japan.
- RIKEN Harima Institute, Spring-8, 1-1-1 Kouto, Sayo, Sayo, Hyogo, 679-5148, Japan.
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