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Systematic determination of disulfide bond reduction potentials reveals a nonequilibrium redox hierarchy in cyanobacteria.

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Title: Systematic determination of disulfide bond reduction potentials reveals a nonequilibrium redox hierarchy in cyanobacteria.
Authors: Tanaka, Kenya1,2,3 tanaka@emerald.kobe-u.ac.jp, Kondo, Akihiko2, Hasunuma, Tomohisa1,2,4,5 hasunuma@port.kobe-u.ac.jp
Source: Proceedings of the National Academy of Sciences of the United States of America. 5/26/2026, Vol. 123 Issue 21, p1-12. 12p.
Subjects: Reduction potential, Cyanobacteria, Mass spectrometry, Photosynthesis, Calvin cycle, Thioredoxin, Disulfides, Cellular control mechanisms
Abstract: Disulfide bonds act as reversible switches that regulate cellular function in nearly all organisms. Their behavior is set by the midpoint potential (Em), yet Em is known for only a small number of sites, mostly in purified proteins studied away from their natural partners. We developed a mass-spectrometry workflow that measures Em directly from native cell lysates. By equilibrating proteins of the cyanobacterium Synechocystis sp. PCC 6803 in defined redox buffers and reading out the oxidation state of individual cysteines, we obtained 368 Em values across the proteome and validated them against purified proteins. A key example is the regulatory protein CP12: its Em in isolation differs strongly from the value measured in lysate and converges only when its physiological partner, thioredoxin, is included, showing that our approach captures the effective potentials that operate inside cells. Combining Em with absolute measurements of cysteine redox state in light and darkness, we mapped intracellular redox "operating points" for Calvin-Benson-Bassham (CBB) cycle enzymes. Phosphoribulokinase sits near thioredoxin, whereas fructose 1,6-bisphosphatase/sedoheptulose 1,7-bisphosphatase (F/SBPase) and CP12 are maintained at more oxidized, nonequilibrium states. These results reveal a hierarchical redox control network in photosynthetic metabolism and provide a general strategy for measuring context-dependent redox switches in living systems. [ABSTRACT FROM AUTHOR]
Copyright of Proceedings of the National Academy of Sciences of the United States of America is the property of National Academy of Sciences and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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  Data: Systematic determination of disulfide bond reduction potentials reveals a nonequilibrium redox hierarchy in cyanobacteria.
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  Data: <searchLink fieldCode="AR" term="%22Tanaka%2C+Kenya%22">Tanaka, Kenya</searchLink><relatesTo>1,2,3</relatesTo><i> tanaka@emerald.kobe-u.ac.jp</i><br /><searchLink fieldCode="AR" term="%22Kondo%2C+Akihiko%22">Kondo, Akihiko</searchLink><relatesTo>2</relatesTo><br /><searchLink fieldCode="AR" term="%22Hasunuma%2C+Tomohisa%22">Hasunuma, Tomohisa</searchLink><relatesTo>1,2,4,5</relatesTo><i> hasunuma@port.kobe-u.ac.jp</i>
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  Data: <searchLink fieldCode="DE" term="%22Reduction+potential%22">Reduction potential</searchLink><br /><searchLink fieldCode="DE" term="%22Cyanobacteria%22">Cyanobacteria</searchLink><br /><searchLink fieldCode="DE" term="%22Mass+spectrometry%22">Mass spectrometry</searchLink><br /><searchLink fieldCode="DE" term="%22Photosynthesis%22">Photosynthesis</searchLink><br /><searchLink fieldCode="DE" term="%22Calvin+cycle%22">Calvin cycle</searchLink><br /><searchLink fieldCode="DE" term="%22Thioredoxin%22">Thioredoxin</searchLink><br /><searchLink fieldCode="DE" term="%22Disulfides%22">Disulfides</searchLink><br /><searchLink fieldCode="DE" term="%22Cellular+control+mechanisms%22">Cellular control mechanisms</searchLink>
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  Data: Disulfide bonds act as reversible switches that regulate cellular function in nearly all organisms. Their behavior is set by the midpoint potential (Em), yet Em is known for only a small number of sites, mostly in purified proteins studied away from their natural partners. We developed a mass-spectrometry workflow that measures Em directly from native cell lysates. By equilibrating proteins of the cyanobacterium Synechocystis sp. PCC 6803 in defined redox buffers and reading out the oxidation state of individual cysteines, we obtained 368 Em values across the proteome and validated them against purified proteins. A key example is the regulatory protein CP12: its Em in isolation differs strongly from the value measured in lysate and converges only when its physiological partner, thioredoxin, is included, showing that our approach captures the effective potentials that operate inside cells. Combining Em with absolute measurements of cysteine redox state in light and darkness, we mapped intracellular redox "operating points" for Calvin-Benson-Bassham (CBB) cycle enzymes. Phosphoribulokinase sits near thioredoxin, whereas fructose 1,6-bisphosphatase/sedoheptulose 1,7-bisphosphatase (F/SBPase) and CP12 are maintained at more oxidized, nonequilibrium states. These results reveal a hierarchical redox control network in photosynthetic metabolism and provide a general strategy for measuring context-dependent redox switches in living systems. [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
  Label:
  Group: Ab
  Data: <i>Copyright of Proceedings of the National Academy of Sciences of the United States of America is the property of National Academy of Sciences and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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RecordInfo BibRecord:
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        Value: 10.1073/pnas.2600150123
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      – Code: eng
        Text: English
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        PageCount: 12
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      – SubjectFull: Reduction potential
        Type: general
      – SubjectFull: Cyanobacteria
        Type: general
      – SubjectFull: Mass spectrometry
        Type: general
      – SubjectFull: Photosynthesis
        Type: general
      – SubjectFull: Calvin cycle
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      – SubjectFull: Thioredoxin
        Type: general
      – SubjectFull: Disulfides
        Type: general
      – SubjectFull: Cellular control mechanisms
        Type: general
    Titles:
      – TitleFull: Systematic determination of disulfide bond reduction potentials reveals a nonequilibrium redox hierarchy in cyanobacteria.
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            NameFull: Tanaka, Kenya
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            NameFull: Kondo, Akihiko
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            NameFull: Hasunuma, Tomohisa
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            – D: 26
              M: 05
              Text: 5/26/2026
              Type: published
              Y: 2026
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