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*

Nature Communications, Published: 03 May 2026

Abstract

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.

原文链接：https://doi.org/10.1038/s41467-026-72738-5