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<p>Iron-limitation is a common stress factor in natural environments. To survive under iron-starved conditions, cyanobacteria overexpress iron stress-induced protein A (IsiA), which is crucial for light-harvesting and photoprotection. Multiple IsiA proteins form a single- or double-layered architecture encircling the photosystem I (PSI) core, forming various PSI-IsiA supercomplexes. The assembly and energy transfer mechanisms of double-layered PSI-IsiA supercomplexes remain unelucidated. Here, we present high-resolution structures of two PSI-IsiA supercomplexes isolated from the cyanobacterium <i>Thermosynechococcus elongatus</i> BP-1 cultured under iron-starved conditions. The PSI<sub>3</sub>-IsiA<sub>43</sub> complex contains a trimeric PSI core surrounded by 43 IsiA subunits assembled into a closed double-ring. The PSI<sub>1</sub>-IsiA<sub>13</sub> complex contains 13 IsiA proteins arranged in a double-layered architecture attached to the monomeric PSI core. Atomic force microscopy demonstrates the presence and distribution of different PSI-IsiA complexes within native thylakoid membranes isolated from iron-starved cells. Our findings provide insights into the structural variability and adaptive mechanisms of PSI-IsiA complexes.</p>

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Structural basis for the assembly and energy transfer between the cyanobacterial PSI core and the double-layered IsiA proteins

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年12月20日

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  • Long Si,
  • Yingyue Zhang,
  • Xiaodong Su,
  • Xuelin Zhao,
  • Xiaomin An,
  • Lu-Ning Liu,
  • Peng Cao,
  • Mei Li

摘要

Iron-limitation is a common stress factor in natural environments. To survive under iron-starved conditions, cyanobacteria overexpress iron stress-induced protein A (IsiA), which is crucial for light-harvesting and photoprotection. Multiple IsiA proteins form a single- or double-layered architecture encircling the photosystem I (PSI) core, forming various PSI-IsiA supercomplexes. The assembly and energy transfer mechanisms of double-layered PSI-IsiA supercomplexes remain unelucidated. Here, we present high-resolution structures of two PSI-IsiA supercomplexes isolated from the cyanobacterium Thermosynechococcus elongatus BP-1 cultured under iron-starved conditions. The PSI3-IsiA43 complex contains a trimeric PSI core surrounded by 43 IsiA subunits assembled into a closed double-ring. The PSI1-IsiA13 complex contains 13 IsiA proteins arranged in a double-layered architecture attached to the monomeric PSI core. Atomic force microscopy demonstrates the presence and distribution of different PSI-IsiA complexes within native thylakoid membranes isolated from iron-starved cells. Our findings provide insights into the structural variability and adaptive mechanisms of PSI-IsiA complexes.