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Fujii S, Kobayashi S, Yoshimi T, Kobayashi Y, Wakai S, Yamanaka M, Sambongi Y. Thermal stability tuning without affecting gas-binding function of Thermochromatium tepidum cytochrome c'. Biosci Biotechnol Biochem 2021; 85:1846-1852. [PMID: 34124760 DOI: 10.1093/bbb/zbab108] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2021] [Accepted: 06/07/2021] [Indexed: 12/17/2022]
Abstract
Hydrogenophilus thermoluteolus, Thermochromatium tepidum, and Allochromatium vinosum, which grow optimally at 52, 49, and 25 °C, respectively, have homologous cytochromes c' (PHCP, TTCP, and AVCP, respectively) exhibiting at least 50% amino acid sequence identity. Here, the thermal stability of the recombinant TTCP protein was first confirmed to be between those of PHCP and AVCP. Structure comparison of the 3 proteins and a mutagenesis study on TTCP revealed that hydrogen bonds and hydrophobic interactions between the heme and amino acid residues were responsible for their stability differences. In addition, PHCP, TTCP, and AVCP and their variants with altered stability similarly bound nitric oxide and carbon oxide, but not oxygen. Therefore, the thermal stability of TTCP together with PHCP and AVCP can be tuned through specific interactions around the heme without affecting their gas-binding function. These cytochromes c' will be useful as specific gas sensor proteins exhibiting a wide thermal stability range.
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Affiliation(s)
- Sotaro Fujii
- Graduate School of Integrated Sciences for Life, Hiroshima University, Hiroshima, Japan
| | - Satoru Kobayashi
- Graduate School of Biosphere Science, Hiroshima University, Hiroshima, Japan
| | - Taisuke Yoshimi
- Graduate School of Integrated Sciences for Life, Hiroshima University, Hiroshima, Japan
| | - Yuji Kobayashi
- Graduate School of Engineering, Osaka University, Osaka, Japan
| | - Satoshi Wakai
- Institute for Extra-Cutting-Edge Science and Technology Avant-Garde Research, Japan Agency for Marine-Earth Science and Technology, Kanagawa, Japan
| | - Masaru Yamanaka
- Graduate School of Science and Technology, Nara Institute of Science and Technology, Nara, Japan
| | - Yoshihiro Sambongi
- Graduate School of Integrated Sciences for Life, Hiroshima University, Hiroshima, Japan
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2
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Sakaguchi R, Fujiyoshi S, Wakai S, Yamanaka M, Sambongi Y. Thermal destabilization mechanism of cytochrome c' from psychrophilic Shewanella violacea. Biosci Biotechnol Biochem 2021; 85:1121-1127. [PMID: 33686411 DOI: 10.1093/bbb/zbab007] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2020] [Accepted: 01/06/2021] [Indexed: 02/01/2023]
Abstract
Cytochrome c' is a nitric oxide (NO)-binding heme protein found in Gram negative bacteria. The thermal stability of psychrophilic Shewanella violacea cytochrome c' (SVCP) is lower than those of its homologues from other 2 psychrophilic Shewanella species, indicating that thermal destabilization mechanism for low-temperature adaptation accumulates in SVCP. In order to understand this mechanism at the amino acid level, here the stability and function of SVCP variants, modeled using the 2 homologues, were examined. The variants exhibited increased stability, and they bound NO similar to the wild type. The vulnerability as to the SVCP stability could be attributed to less hydrogen bond at the subunit interface, more flexible loop structure, and less salt bridge on the protein surface, which appear to be its destabilization mechanism. This study provides an example for controlling stability without spoiling function in psychrophilic proteins.
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Affiliation(s)
- Riku Sakaguchi
- Graduate School of Integrated Sciences for Life, Hiroshima University, Higashi-Hiroshima, Japan
| | - So Fujiyoshi
- Office of Academic Research and Industry-Government Collaboration, Hiroshima University, Higashi-Hiroshima, Japan
| | - Satoshi Wakai
- Institute for Extra-Cutting-Edge Science and Technology Avant-Garde Research, Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan
| | - Masaru Yamanaka
- Graduate School of Science and Technology, Nara Institute of Science and Technology, Ikoma, Japan
| | - Yoshihiro Sambongi
- Graduate School of Integrated Sciences for Life, Hiroshima University, Higashi-Hiroshima, Japan
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3
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Yamanaka M, Nakayama R, Fujii S, Wakai S, Sambongi Y, Hirota S. Conferment of CO-Controlled Dimer–Monomer Transition Property to Thermostable Cytochromec′ by Mutation in the Subunit–Subunit Interface. BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 2019. [DOI: 10.1246/bcsj.20180311] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- Masaru Yamanaka
- Division of Materials Science, Graduate School of Science and Technology, Nara Institute of Science and Technology, 8916-5 Takayama-cho, Ikoma, Nara 630-0192, Japan
| | - Ryoko Nakayama
- Division of Materials Science, Graduate School of Science and Technology, Nara Institute of Science and Technology, 8916-5 Takayama-cho, Ikoma, Nara 630-0192, Japan
| | - Sotaro Fujii
- Graduate School of Biosphere Science, Hiroshima University, 1-4-4 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8528, Japan
| | - Satoshi Wakai
- Graduate School of Science, Technology and Innovation, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe, Hyogo 657-8501, Japan
| | - Yoshihiro Sambongi
- Graduate School of Biosphere Science, Hiroshima University, 1-4-4 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8528, Japan
| | - Shun Hirota
- Division of Materials Science, Graduate School of Science and Technology, Nara Institute of Science and Technology, 8916-5 Takayama-cho, Ikoma, Nara 630-0192, Japan
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Fujimori K, Fujii S, Lisdiana L, Wakai S, Yagi H, Sambongi Y. Differences in biochemical properties of two 5'-nucleotidases from deep- and shallow-sea Shewanella species under various harsh conditions. Biosci Biotechnol Biochem 2019; 83:1085-1093. [PMID: 30764715 DOI: 10.1080/09168451.2019.1578641] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Deep-sea Shewanella violacea 5'-nucleotidase (SVNTase) activity exhibited higher NaCl tolerance than that of a shallow-sea Shewanella amazonensis homologue (SANTase), the sequence identity between them being 70.4%. Here, SVNTase exhibited higher activity than SANTase with various inorganic salts, similar to the difference in their NaCl tolerance. In contrast, SVNTase activity decreased with various organic solvents, while SANTase activity was retained with the same concentrations of the solvents. Therefore, SVNTase is more robust than SANTase with inorganic salts, but more vulnerable with organic solvents. As to protein stability, SANTase was more stable against organic solvents and heat than SVNTase, which correlated with the differences in their enzymatic activities. We also found that SANTase retained higher activity for three weeks than SVNTase did in the presence of glycerol. These findings will facilitate further application of these enzymes as appropriate biological catalysts under various harsh conditions. Abbreviations: NTase: 5'-nucleotidase; SANTase: Shewanella amazonensis 5'-nucleotidase; SVNTase: Shewanella violacea 5'-nucleotidase; CD: circular dichroism.
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Affiliation(s)
- Kiko Fujimori
- a Graduate School of Biosphere Science , Hiroshima University , Higashi-Hiroshima , Japan
| | - Sotaro Fujii
- a Graduate School of Biosphere Science , Hiroshima University , Higashi-Hiroshima , Japan
| | - Lisa Lisdiana
- a Graduate School of Biosphere Science , Hiroshima University , Higashi-Hiroshima , Japan.,b Department of Biology , Universitas Negeri Surabaya, Kampus Unesa Ketintang , Surabaya , Indonesia
| | - Satoshi Wakai
- c Graduate School of Science, Technology, and Innovation , Kobe University , Kobe , Japan
| | - Hisashi Yagi
- d Department of Chemistry and Biotechnology, Graduate School of Sustainability Science , Tottori University , Tottori , Japan.,e Center for Research on Green Sustainable Chemistry , Tottori University , Tottori , Japan
| | - Yoshihiro Sambongi
- a Graduate School of Biosphere Science , Hiroshima University , Higashi-Hiroshima , Japan
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5
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Stability of cytochromes c′ from psychrophilic and piezophilic Shewanella species: implications for complex multiple adaptation to low temperature and high hydrostatic pressure. Extremophiles 2019; 23:239-248. [DOI: 10.1007/s00792-019-01077-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2018] [Accepted: 01/13/2019] [Indexed: 10/27/2022]
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Yamane-Koshizawa D, Fujii S, Maruno T, Kobayashi Y, Yamanaka M, Wakai S, Sambongi Y. Stabilization of mesophilic Allochromatium vinosum cytochrome c′ through specific mutations modeled by a thermophilic homologue. Biosci Biotechnol Biochem 2018; 82:304-311. [DOI: 10.1080/09168451.2017.1419856] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Abstract
AVCP cytochrome c′ from mesophilic Allochromatium vinosum exhibits lower stability than a thermophilic counterpart, Hydrogenophilus thermoluteolus cytochrome c′ (PHCP), in which the six specific amino acid residues that are not conserved in AVCP are responsible for its stability. Here we measured the stability of AVCP variants carrying these specific residues instead of the original AVCP ones. Among the six single AVCP variants, all of which formed a dimeric structure similar to that of the wild-type, three were successfully stabilized compared with the wild-type, while one showed lower stability than the wild-type. In addition, the most stabilized and destabilized AVCP variants could bind CO, similar to the wild-type. These results indicated that mesophilic AVCP could be stabilized through specific three mutations modeled by the thermophilic counterpart, PHCP, without changing the CO binding ability.
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Affiliation(s)
| | - Sotaro Fujii
- Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima, Japan
- Global Career Design Center, Hiroshima University, Higashi-Hiroshima, Japan
| | - Takahiro Maruno
- Graduate School of Engineering, Osaka University, Suita, Japan
| | - Yuji Kobayashi
- Graduate School of Engineering, Osaka University, Suita, Japan
| | - Masaru Yamanaka
- Graduate School of Materials Science, Nara Institute of Science and Technology, Ikoma, Japan
| | - Satoshi Wakai
- Graduate School of Science Technology and Innovation, Kobe University, Kobe, Japan
| | - Yoshihiro Sambongi
- Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima, Japan
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Fujii S, Oki H, Kawahara K, Yamane D, Yamanaka M, Maruno T, Kobayashi Y, Masanari M, Wakai S, Nishihara H, Ohkubo T, Sambongi Y. Structural and functional insights into thermally stable cytochrome c' from a thermophile. Protein Sci 2017; 26:737-748. [PMID: 28097774 PMCID: PMC5368077 DOI: 10.1002/pro.3120] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2016] [Revised: 01/06/2017] [Accepted: 01/09/2017] [Indexed: 11/10/2022]
Abstract
Thermophilic Hydrogenophilus thermoluteolus cytochrome c′ (PHCP) exhibits higher thermal stability than a mesophilic counterpart, Allochromatium vinosum cytochrome c′ (AVCP), which has a homo‐dimeric structure and ligand‐binding ability. To understand the thermal stability mechanism and ligand‐binding ability of the thermally stable PHCP protein, the crystal structure of PHCP was first determined. It formed a homo‐dimeric structure, the main chain root mean square deviation (rmsd) value between PHCP and AVCP being 0.65 Å. In the PHCP structure, six specific residues appeared to strengthen the heme‐related and subunit–subunit interactions, which were not conserved in the AVCP structure. PHCP variants having altered subunit–subunit interactions were more severely destabilized than ones having altered heme‐related interactions. The PHCP structure further revealed a ligand‐binding channel and a penta‐coordinated heme, as observed in the AVCP protein. A spectroscopic study clearly showed that some ligands were bound to the PHCP protein. It is concluded that the dimeric PHCP from the thermophile is effectively stabilized through heme‐related and subunit–subunit interactions with conservation of the ligand‐binding ability. Brief Summary We report the X‐ray crystal structure of cytochrome c′ (PHCP) from thermophilic Hydrogenophilus thermoluteolus. The high thermal stability of PHCP was attributed to heme‐related and subunit–subunit interactions, which were confirmed by a mutagenesis study. The ligand‐binding ability of PHCP was examined by spectrophotometry. PHCP acquired the thermal stability with conservation of the ligand‐binding ability. This study furthers the understanding of the stability and function of cytochromes c. PDB Code(s): 5B3I
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Affiliation(s)
- Sotaro Fujii
- Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima, Hiroshima, Japan
| | - Hiroya Oki
- Graduate School of Pharmaceutical Sciences, Osaka University, Yamadaoka, Suita, Osaka, Japan
| | - Kazuki Kawahara
- Graduate School of Pharmaceutical Sciences, Osaka University, Yamadaoka, Suita, Osaka, Japan
| | - Daisuke Yamane
- Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima, Hiroshima, Japan
| | - Masaru Yamanaka
- Graduate School of Materials Science, Nara Institute of Science and Technology, Ikoma, Nara, Japan
| | - Takahiro Maruno
- Graduate School of Engineering, Osaka University, Yamadaoka, Suita, Osaka, Japan
| | - Yuji Kobayashi
- Graduate School of Engineering, Osaka University, Yamadaoka, Suita, Osaka, Japan
| | - Misa Masanari
- Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima, Hiroshima, Japan
| | - Satoshi Wakai
- Graduate School of Science, Technology, and Innovation, Kobe University, Rokkodai, Kobe, Hyogo, Japan
| | | | - Tadayasu Ohkubo
- Graduate School of Pharmaceutical Sciences, Osaka University, Yamadaoka, Suita, Osaka, Japan
| | - Yoshihiro Sambongi
- Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima, Hiroshima, Japan
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Yamanaka M, Hoshizumi M, Nagao S, Nakayama R, Shibata N, Higuchi Y, Hirota S. Formation and carbon monoxide-dependent dissociation of Allochromatium vinosum cytochrome c' oligomers using domain-swapped dimers. Protein Sci 2017; 26:464-474. [PMID: 27883268 PMCID: PMC5326568 DOI: 10.1002/pro.3090] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2016] [Revised: 11/18/2016] [Accepted: 11/18/2016] [Indexed: 12/12/2022]
Abstract
The number of artificial protein supramolecules has been increasing; however, control of protein oligomer formation remains challenging. Cytochrome c' from Allochromatium vinosum (AVCP) is a homodimeric protein in its native form, where its protomer exhibits a four-helix bundle structure containing a covalently bound five-coordinate heme as a gas binding site. AVCP exhibits a unique reversible dimer-monomer transition according to the absence and presence of CO. Herein, domain-swapped dimeric AVCP was constructed and utilized to form a tetramer and high-order oligomers. The X-ray crystal structure of oxidized tetrameric AVCP consisted of two monomer subunits and one domain-swapped dimer subunit, which exchanged the region containing helices αA and αB between protomers. The active site structures of the domain-swapped dimer subunit and monomer subunits in the tetramer were similar to those of the monomer subunits in the native dimer. The subunit-subunit interactions at the interfaces of the domain-swapped dimer and monomer subunits in the tetramer were also similar to the subunit-subunit interaction in the native dimer. Reduced tetrameric AVCP dissociated to a domain-swapped dimer and two monomers upon CO binding. Without monomers, the domain-swapped dimers formed tetramers, hexamers, and higher-order oligomers in the absence of CO, whereas the oligomers dissociated to domain-swapped dimers in the presence of CO, demonstrating that the domain-swapped dimer maintains the CO-induced subunit dissociation behavior of native ACVP. These results suggest that protein oligomer formation may be controlled by utilizing domain swapping for a dimer-monomer transition protein.
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Affiliation(s)
- Masaru Yamanaka
- Graduate School of Materials ScienceNara Institute of Science and Technology8916‐5 Takayama, IkomaNara630‐0192Japan
| | - Makoto Hoshizumi
- Graduate School of Materials ScienceNara Institute of Science and Technology8916‐5 Takayama, IkomaNara630‐0192Japan
| | - Satoshi Nagao
- Graduate School of Materials ScienceNara Institute of Science and Technology8916‐5 Takayama, IkomaNara630‐0192Japan
| | - Ryoko Nakayama
- Graduate School of Materials ScienceNara Institute of Science and Technology8916‐5 Takayama, IkomaNara630‐0192Japan
| | - Naoki Shibata
- Department of Life ScienceGraduate School of Life Science, University of Hyogo3‐2‐1 Koto, Kamigori‐cho, Ako‐gunHyogo678‐1297Japan
- RIKEN SPring‐8 Center1‐1‐1 Koto, Sayo‐cho, Sayo‐gunHyogo679‐5148Japan
| | - Yoshiki Higuchi
- Department of Life ScienceGraduate School of Life Science, University of Hyogo3‐2‐1 Koto, Kamigori‐cho, Ako‐gunHyogo678‐1297Japan
- RIKEN SPring‐8 Center1‐1‐1 Koto, Sayo‐cho, Sayo‐gunHyogo679‐5148Japan
| | - Shun Hirota
- Graduate School of Materials ScienceNara Institute of Science and Technology8916‐5 Takayama, IkomaNara630‐0192Japan
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Kato Y, Fujii S, Kuribayashi TA, Masanari M, Sambongi Y. Thermal stability of cytochrome c′ from mesophilic Shewanella amazonensis. Biosci Biotechnol Biochem 2015; 79:1125-9. [DOI: 10.1080/09168451.2015.1015956] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Abstract
Cytochrome c′ (SACP) from mesophilic Shewanella amazonensis, growing optimally at 37 °C, was thermally more stable than cytochrome c′ (AVCP) from mesophilic Allochromatium vinosum, growing optimally at 25 °C. In contrast, SACP was less stable than cytochrome c′ (PHCP) from thermophilic Hydrogenophilus thermoluteolus, growing optimally at 52 °C. Although only 28% of the SACP amino acid sequence was identical to those of AVCP and PHCP, the latter two being 55% identical, the overall main chain structures of the three cytochromes c′ were similar, and SACP exhibited thermal stability intermediate between those of AVCP and PHCP. For these three proteins, the higher the stability is, the lesser the number of Gly residues in the putative α-helical regions is. Cytochromes c′ including the present three are suitable for examining the protein stabilization mechanisms, because they are structurally similar and available from environments with a wide range of temperatures.
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Affiliation(s)
- Yuki Kato
- Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima, Japan
| | - Sotaro Fujii
- Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima, Japan
| | - Taka-aki Kuribayashi
- Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima, Japan
| | - Misa Masanari
- Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima, Japan
| | - Yoshihiro Sambongi
- Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima, Japan
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Kimura Y, Kasuga S, Unno M, Furusawa T, Osoegawa S, Sasaki Y, Ohno T, Wang-Otomo ZY. The roles of C-terminal residues on the thermal stability and local heme environment of cytochrome c' from the thermophilic purple sulfur bacterium Thermochromatium tepidum. PHOTOSYNTHESIS RESEARCH 2015; 124:19-29. [PMID: 25519852 DOI: 10.1007/s11120-014-0069-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/17/2014] [Accepted: 12/11/2014] [Indexed: 06/04/2023]
Abstract
A soluble cytochrome (Cyt) c' from thermophilic purple sulfur photosynthetic bacterium Thermochromatium (Tch.) tepidum exhibits marked thermal tolerance compared with that from the closely related mesophilic counterpart Allochromatium vinosum. Here, we focused on the difference in the C-terminal region of the two Cyts c' and examined the effects of D131 and R129 mutations on the thermal stability and local heme environment of Cyt c' by differential scanning calorimetry (DSC) and resonance Raman (RR) spectroscopy. In the oxidized forms, D131K and D131G mutants exhibited denaturing temperatures significantly lower than that of the recombinant control Cyt c'. In contrast, R129K and R129A mutants denatured at nearly identical temperatures with the control Cyt c', indicating that the C-terminal D131 is an important residue maintaining the enhanced thermal stability of Tch. tepidum Cyt c'. The control Cyt c' and all of the mutants increased their thermal stability upon the reduction. Interestingly, D131K exhibited narrow DSC curves and unusual thermodynamic parameters in both redox states. The RR spectra of the control Cyt c' exhibited characteristic bands at 1,635 and 1,625 cm(-1), ascribed to intermediate spin (IS) and high spin (HS) states, respectively. The IS/HS distribution was differently affected by the D131 and R129 mutations and pH changes. Furthermore, R129 mutants suggested the lowering of their redox potentials. These results strongly indicate that the D131 and R129 residues play significant roles in maintaining the thermal stability and modulating the local heme environment of Tch. tepidum Cyt c'.
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Affiliation(s)
- Yukihiro Kimura
- Department of Agrobioscience, Graduate School of Agricultural Science, Kobe University, Nada, Kobe, 657-8501, Japan,
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Fujii S, Masanari M, Yamanaka M, Wakai S, Sambongi Y. High stability of apo-cytochrome c' from thermophilic Hydrogenophilus thermoluteolus. Biosci Biotechnol Biochem 2014; 78:1191-4. [PMID: 25229856 DOI: 10.1080/09168451.2014.912120] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Apo-cytochomes c without heme are usually unstructured. Here we showed that apo-form of thermophilic Hydrogenophilus thermoluteolus cytochrome c' (PHCP) was a monomeric protein with high helix content. Apo-PHCP was thermally stable, possibly due to the hydrophobic residues and ion pairs. PHCP is the first example of a structured apo-cytochrome c', which will expand our view of hemoprotein structure formation.
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Affiliation(s)
- Sotaro Fujii
- a Graduate School of Biosphere Science , Hiroshima University , Higashi-Hiroshima , Japan
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