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<p>Starch serves as a vital energy reserve in plants. During its biosynthesis, malto-oligosaccharides (MOS) are essential primers. One of the key pathways for MOS production involves plastidial α-glucan phosphorylase (PHS1/Pho1) and disproportionating enzyme (DPE1). However, the functional relationship between these enzymes is unclear. Here, we demonstrate that rice PHS1 and DPE1 assemble into a multimeric complex. Cryo-EM structures of the PHS1-DPE1 complex reveal an assembly mechanism and suggest a potential substrate tunnel. Biochemical assays show the complex dramatically enhances catalytic efficiency over individual enzymes. Single-molecule fluorescence resonance energy transfer (smFRET) visualizes conformational dynamics, enabling rapid substrate transfer between the enzymes. We further identify the unique L80 loop in PHS1 as a potential regulator. Its deletion reduces catalytic efficiency and prolongs conformational state lifetimes during substrate transfer, thereby reducing the production of longer MOSs. Our findings establish that the PHS1-DPE1 complex facilitates efficient MOS primer synthesis through efficient substrate transfer or diffusion between the two enzymes, providing mechanistic insight into a critical step of starch biosynthesis with agronomic implications.</p>

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The plastidial PHS1-DPE1 complex drives efficient malto-oligosaccharides synthesis in rice starch metabolism

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年5月3日

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  • Jian Liu,
  • Xinru Wu,
  • Haitao He,
  • Xi Yang,
  • Yuanhuai Hu,
  • Fei Zhang,
  • Rong Fan,
  • Xuecui Wang,
  • Shenao Yang,
  • Lian Xiong,
  • Delin Zhang,
  • Ping Yin,
  • Jianping Guo,
  • Zhu Liu,
  • Junjie Yan

摘要

Starch serves as a vital energy reserve in plants. During its biosynthesis, malto-oligosaccharides (MOS) are essential primers. One of the key pathways for MOS production involves plastidial α-glucan phosphorylase (PHS1/Pho1) and disproportionating enzyme (DPE1). However, the functional relationship between these enzymes is unclear. Here, we demonstrate that rice PHS1 and DPE1 assemble into a multimeric complex. Cryo-EM structures of the PHS1-DPE1 complex reveal an assembly mechanism and suggest a potential substrate tunnel. Biochemical assays show the complex dramatically enhances catalytic efficiency over individual enzymes. Single-molecule fluorescence resonance energy transfer (smFRET) visualizes conformational dynamics, enabling rapid substrate transfer between the enzymes. We further identify the unique L80 loop in PHS1 as a potential regulator. Its deletion reduces catalytic efficiency and prolongs conformational state lifetimes during substrate transfer, thereby reducing the production of longer MOSs. Our findings establish that the PHS1-DPE1 complex facilitates efficient MOS primer synthesis through efficient substrate transfer or diffusion between the two enzymes, providing mechanistic insight into a critical step of starch biosynthesis with agronomic implications.