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<p>Scytonemin, a UV-protective pigment produced by cyanobacteria, is essential for microbial survival under extreme solar radiation. Recent studies suggest its structural analog, scytonemin imine, may serve as a biosynthetic marker for cyanobacteria exposed to intense light. Here, we present a structural revision, revealing scytonemin imine as a cyclic hydropyrrolo[2,3-<i>b</i>]indole, rather than the previously proposed primary imine. This reassignment is supported by 1D and 2D NMR, Q-TOF mass spectrometry, confirmatory synthesis, and DFT calculations. Our synthesis demonstrates that scytonemin converts to scytonemin imine under mild conditions–ammonia and acetone exposure–suggesting the imine adduct is likely an artifact of isolation. However, our findings also indicate that this artifact may reveal a previously unrecognized <i>in-vivo</i> state of scytonemin, which is released upon condensation with acetone. This reactivity uncovers a new chromism within the scytonemin scaffold, supporting the idea that biogenic scytonemin analogs may filter visible light to regulate photosynthesis and protect against ROS-mediated photodamage during high light exposure or desiccation. This chromatic transformation highlights scytonemin’s structural adaptability, offering insight into its role as a protective pigment in ancient and modern cyanobacteria and its relevance for understanding microbial adaptation to extreme environments.</p>

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Structure revision of scytonemin imine and its relationship to scytonemin chromism and cyanobacterial adaptability

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年7月15日

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  • Garrett E. Larson,
  • Tanzil Mahmud,
  • Ilya D. Dergachev,
  • Casey S. Philbin,
  • Yingshi Feng,
  • Celso R. de Oliveira,
  • Henry J. Sun,
  • Matthew J. Tucker,
  • Sergey A. Varganov,
  • Christopher S. Jeffrey

摘要

Scytonemin, a UV-protective pigment produced by cyanobacteria, is essential for microbial survival under extreme solar radiation. Recent studies suggest its structural analog, scytonemin imine, may serve as a biosynthetic marker for cyanobacteria exposed to intense light. Here, we present a structural revision, revealing scytonemin imine as a cyclic hydropyrrolo[2,3-b]indole, rather than the previously proposed primary imine. This reassignment is supported by 1D and 2D NMR, Q-TOF mass spectrometry, confirmatory synthesis, and DFT calculations. Our synthesis demonstrates that scytonemin converts to scytonemin imine under mild conditions–ammonia and acetone exposure–suggesting the imine adduct is likely an artifact of isolation. However, our findings also indicate that this artifact may reveal a previously unrecognized in-vivo state of scytonemin, which is released upon condensation with acetone. This reactivity uncovers a new chromism within the scytonemin scaffold, supporting the idea that biogenic scytonemin analogs may filter visible light to regulate photosynthesis and protect against ROS-mediated photodamage during high light exposure or desiccation. This chromatic transformation highlights scytonemin’s structural adaptability, offering insight into its role as a protective pigment in ancient and modern cyanobacteria and its relevance for understanding microbial adaptation to extreme environments.