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<p>FliP, FliQ, and FliR form the membrane-embedded protein-export channel that powers bacterial flagellar assembly. How they assemble into a functional export channel remains unclear. Here we combine topological mapping, cryo-EM image analysis, and biochemical assays to investigate the assembly mechanism of the FliPQR complex. PhoA fusion assays suggest that membrane-spanning helices of each subunit become repositioned toward the periplasm upon complex assembly, supporting substantial topological remodeling. FliP alone forms higher-order oligomers, with pentameric species predominating and putative hexameric species appearing less stable. FliR associates with the FliP assembly to form a stable FliPR complex. The FliQ-like structural element in FliR contributes to recruitment of the first FliQ subunit and promotes stable FliQ assembly. Together, these findings support a working model in which hierarchical assembly of the FliPQR complex is accompanied by substantial topological remodeling, providing a framework for understanding export channel biogenesis in flagellar and related type III secretion systems.</p><p></p>

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Dynamic topological remodeling underlies assembly of the flagellar protein-export channel FliPQR complex

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年8月3日

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  • Miki Kinoshita,
  • Akihiro Kawamoto,
  • Keiichi Namba,
  • Tohru Minamino

摘要

FliP, FliQ, and FliR form the membrane-embedded protein-export channel that powers bacterial flagellar assembly. How they assemble into a functional export channel remains unclear. Here we combine topological mapping, cryo-EM image analysis, and biochemical assays to investigate the assembly mechanism of the FliPQR complex. PhoA fusion assays suggest that membrane-spanning helices of each subunit become repositioned toward the periplasm upon complex assembly, supporting substantial topological remodeling. FliP alone forms higher-order oligomers, with pentameric species predominating and putative hexameric species appearing less stable. FliR associates with the FliP assembly to form a stable FliPR complex. The FliQ-like structural element in FliR contributes to recruitment of the first FliQ subunit and promotes stable FliQ assembly. Together, these findings support a working model in which hierarchical assembly of the FliPQR complex is accompanied by substantial topological remodeling, providing a framework for understanding export channel biogenesis in flagellar and related type III secretion systems.