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<p>The bacterial phosphoenolpyruvate:sugar phosphotransferase system (PTS) catalyzes the transport and phosphorylation of carbohydrates. The glucitol (Gut) PTS transporter from <i>Escherichia coli</i> has often been discussed in relation to the Glucose–Fructose–Lactose (GFL) superfamily, although other work has suggested that it may instead form a separate PTS superfamily. This uncertainty is linked to its unusual genetic organization, in which the transmembrane IIC domain is divided into two polypeptides (IIC1/GutE and IIC2/GutA). Here, we present the cryo-electron microscopy (cryo-EM) structure of the complete Gut transporter, which resolves this discrepancy by revealing a homotrimeric architecture for its transmembrane domain—a fold unprecedented among sugar-transporting PTS permeases. This structural evidence supports the view that the Gut family represents a distinct PTS superfamily. Within the trimer, the protomers are captured in inward-facing and inward-occluded conformations, providing a structural basis for an alternating-access transport mechanism. Furthermore, the structure suggests a unique in-trans phosphotransfer pathway between the IIB and IIC domains of adjacent subunits and identifies the substrate-binding pocket at the GutA/GutE interface. Our work redefines the structural landscape of PTS transporters and provides a mechanistic framework for sugar transport by this unique trimeric porter.</p>

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A trimeric architecture reveals the glucitol PTS transporter as a distinct superfamily

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年3月10日

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  • Tingyue Deng,
  • Xueli Liu,
  • Jianwei Zeng,
  • Xiaofei Ge,
  • Jiawei Wang

摘要

The bacterial phosphoenolpyruvate:sugar phosphotransferase system (PTS) catalyzes the transport and phosphorylation of carbohydrates. The glucitol (Gut) PTS transporter from Escherichia coli has often been discussed in relation to the Glucose–Fructose–Lactose (GFL) superfamily, although other work has suggested that it may instead form a separate PTS superfamily. This uncertainty is linked to its unusual genetic organization, in which the transmembrane IIC domain is divided into two polypeptides (IIC1/GutE and IIC2/GutA). Here, we present the cryo-electron microscopy (cryo-EM) structure of the complete Gut transporter, which resolves this discrepancy by revealing a homotrimeric architecture for its transmembrane domain—a fold unprecedented among sugar-transporting PTS permeases. This structural evidence supports the view that the Gut family represents a distinct PTS superfamily. Within the trimer, the protomers are captured in inward-facing and inward-occluded conformations, providing a structural basis for an alternating-access transport mechanism. Furthermore, the structure suggests a unique in-trans phosphotransfer pathway between the IIB and IIC domains of adjacent subunits and identifies the substrate-binding pocket at the GutA/GutE interface. Our work redefines the structural landscape of PTS transporters and provides a mechanistic framework for sugar transport by this unique trimeric porter.