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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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Kouyama T, Ihara K. Two substates in the O intermediate of the light-driven proton pump archaerhodopsin-2. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2022; 1864:183919. [PMID: 35304864 DOI: 10.1016/j.bbamem.2022.183919] [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: 02/16/2022] [Accepted: 03/07/2022] [Indexed: 06/14/2023]
Abstract
The proton pumping cycle of archaerhodopsin-2 (aR2) was investigated over a wide pH range and at different salt concentrations. We have found that two substates, which are spectroscopically and kinetically distinguishable, occur in the O intermediate. The first O-intermediate (O1) absorbs maximumly at ~580 nm, whereas the late O-intermediate (O2) absorbs maximumly at 605 nm. At neutral pH, O1 is in rapid equilibrium with the N intermediate. When the medium pH is increased, O1 becomes less stable than N and, in proportion to the amount of O1 in the dynamic equilibrium between N and O1, the formation rate of O2 decreases. By contrast, the decay rate of O2 increases ~100 folds when the pH of a low-salt membrane suspension is increased from 5.5 to 7.5 or when the salt concentration is increased to 2 M KCl. Together with our recent study on two substates in the O intermediate of bacteriorhodopsin (bR), the present study suggests that the thermally activated re-isomerization of the retinylidene chromophore into the initial all-trans configuration takes place in the O1-to-O2 transition; that is, O1 contains a distorted 13-cis chromophore. It is also found that the pKa value of the key ionizable residue (Asp101aR2, Asp96bR) in the proton uptake channel is elevated in the O1 state of aR2 as compared to the O1 state of bR. This implies that the structural property of O1 in the aR2 photocycle can be investigated over a wide pH range.
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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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Tamogami J, Kikukawa T, Ohkawa K, Ohsawa N, Nara T, Demura M, Miyauchi S, Kimura-Someya T, Shirouzu M, Yokoyama S, Shimono K, Kamo N. Interhelical interactions between D92 and C218 in the cytoplasmic domain regulate proton uptake upon N-decay in the proton transport of Acetabularia rhodopsin II. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 2018; 183:35-45. [PMID: 29684719 DOI: 10.1016/j.jphotobiol.2018.04.012] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/22/2017] [Revised: 04/07/2018] [Accepted: 04/07/2018] [Indexed: 01/01/2023]
Abstract
Acetabularia rhodopsin II (ARII or Ace2), an outward light-driven algal proton pump found in the giant unicellular marine alga Acetabularia acetabulum, has a unique property in the cytoplasmic (CP) side of its channel. The X-ray crystal structure of ARII in a dark state suggested the formation of an interhelical hydrogen bond between C218ARII and D92ARII, an internal proton donor to the Schiff base (Wada et al., 2011). In this report, we investigated the photocycles of two mutants at position C218ARII: C218AARII which disrupts the interaction with D92ARII, and C218SARII which potentially forms a stronger hydrogen bond. Both mutants exhibited slower photocycles compared to the wild-type pump. Together with several kinetic changes of the photoproducts in the first half of the photocycle, these replacements led to specific retardation of the N-to-O transition in the second half of the photocycle. In addition, measurements of the flash-induced proton uptake and release using a pH-sensitive indium-tin oxide electrode revealed a concomitant delay in the proton uptake. These observations strongly suggest the importance of a native weak hydrogen bond between C218ARII and D92ARII for proper proton translocation in the CP channel during N-decay. A putative role for the D92ARII-C218ARII interhelical hydrogen bond in the function of ARII is discussed.
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Affiliation(s)
- Jun Tamogami
- College of Pharmaceutical Sciences, Matsuyama University, Matsuyama, Ehime 790-8578, Japan.
| | - Takashi Kikukawa
- Faculty of Advanced Life Science, Hokkaido University, Sapporo 060-0810, Japan; Global Station for Soft Matter, Global Institution for Collaborative Research and Education, Hokkaido University, Sapporo 001-0021, Japan
| | - Keisuke Ohkawa
- College of Pharmaceutical Sciences, Matsuyama University, Matsuyama, Ehime 790-8578, Japan
| | - Noboru Ohsawa
- RIKEN Systems and Structural Biology Center, Yokohama 230-0045, Japan; RIKEN Center for Life Science Technologies, Yokohama 230-0045, Japan
| | - Toshifumi Nara
- College of Pharmaceutical Sciences, Matsuyama University, Matsuyama, Ehime 790-8578, Japan
| | - Makoto Demura
- Faculty of Advanced Life Science, Hokkaido University, Sapporo 060-0810, Japan; Global Station for Soft Matter, Global Institution for Collaborative Research and Education, Hokkaido University, Sapporo 001-0021, Japan
| | - Seiji Miyauchi
- College of Pharmaceutical Sciences, Matsuyama University, Matsuyama, Ehime 790-8578, Japan; Graduate School of Pharmaceutical Sciences, Toho University, Funabashi, Chiba 274-8510, Japan
| | - Tomomi Kimura-Someya
- RIKEN Systems and Structural Biology Center, Yokohama 230-0045, Japan; RIKEN Center for Life Science Technologies, Yokohama 230-0045, Japan
| | - Mikako Shirouzu
- RIKEN Systems and Structural Biology Center, Yokohama 230-0045, Japan; RIKEN Center for Life Science Technologies, Yokohama 230-0045, Japan
| | - Shigeyuki Yokoyama
- RIKEN Systems and Structural Biology Center, Yokohama 230-0045, Japan; RIKEN Structural Biology Laboratory, Yokohama 230-0045, Japan
| | - Kazumi Shimono
- College of Pharmaceutical Sciences, Matsuyama University, Matsuyama, Ehime 790-8578, Japan; Graduate School of Pharmaceutical Sciences, Toho University, Funabashi, Chiba 274-8510, Japan
| | - Naoki Kamo
- College of Pharmaceutical Sciences, Matsuyama University, Matsuyama, Ehime 790-8578, Japan; Faculty of Advanced Life Science, Hokkaido University, Sapporo 060-0810, Japan
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Dai G, Geng X, Chaoluomeng, Tamogami J, Kikukawa T, Demura M, Kamo N, Iwasa T. Photocycle of Sensory Rhodopsin II from Halobacterium salinarum (HsSRII): Mutation of D103 Accelerates M Decay and Changes the Decay Pathway of a 13-cis O-like Species. Photochem Photobiol 2018. [PMID: 29512821 DOI: 10.1111/php.12917] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Aspartic acid 103 (D103) of sensory rhodopsin II from Halobacterium salinarum (HsSRII, or also called phoborhodopsin) corresponds to D115 of bacteriorhodopsin (BR). This amino acid residue is functionally important in BR. This work reveals that a substitution of D103 with asparagine (D103N) or glutamic acid (D103E) can cause large changes in HsSRII photocycle. These changes include (1) shortened lifetime of the M intermediate in the following order: the wild-type > D103N > D103E; (2) altered decay pathway of a 13-cis O-like species. The 13-cis O-like species, tentatively named Px, was detected in HsSRII photocycle. Px appeared to undergo branched reactions at 0°C, leading to a recovery of the unphotolyzed state and formation of a metastable intermediate, named P370, that slowly decayed to the unphotolyzed state at room temperature. In wild-type HsSRII at 0°C, Px mainly decayed to the unphotolyzed state, and the decay reaction toward P370 was negligible. In mutant D103E at 0°C, Px decayed to P370, while the recovery of the unphotolyzed state became unobservable. In mutant D103N, the two reactions proceeded at comparable rates. Thus, D103 of HsSRII may play an important role in regulation of the photocycle of HsSRII.
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Affiliation(s)
- Gang Dai
- College of Chemistry and Environmental Science, Inner Mongolia Normal University, Hohhot, 010018, China
| | - Xiong Geng
- Division of Engineering, Muroran Institute of Technology, Muroran, 050-8585, Japan
| | - Chaoluomeng
- Division of Engineering, Muroran Institute of Technology, Muroran, 050-8585, Japan
| | - Jun Tamogami
- College of Pharmaceutical Science, Matsuyama University, Matsuyama, 790-8578, Japan
| | - Takashi Kikukawa
- Faculty of Advanced Life Science, Hokkaido University, Sapporo, 060-0810, Japan.,Global Station for Soft Matter, Global Institution for Collaborative Research and Education, Hokkaido University, Sapporo, 001-0021, Japan
| | - Makoto Demura
- Faculty of Advanced Life Science, Hokkaido University, Sapporo, 060-0810, Japan.,Global Station for Soft Matter, Global Institution for Collaborative Research and Education, Hokkaido University, Sapporo, 001-0021, Japan
| | - Naoki Kamo
- Faculty of Advanced Life Science, Hokkaido University, Sapporo, 060-0810, Japan
| | - Tatsuo Iwasa
- Division of Engineering, Muroran Institute of Technology, Muroran, 050-8585, Japan
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