# Osaka team resolves cryoEM structure of Salmonella P-ring on an elongated flagellar rod

- Published: 2026-11-09 03:30 UTC
- Section: Life & Health › Biology & biochemistry
- Tags: bacterial flagellar motor, LP-ring bushing, P-ring structure, cryoEM single particle analysis, FlgI FlgH FlgG, flagellar rod, self-assembly of nanomachines, Salmonella flagellum
- URL: https://realtech.media/news/rt-44f578cbc398f28c332cbd02_osaka_team_resolves/

**The P-ring binds the rod as a slightly elliptical, tilted ring. L-ring assembly then forces it off, leaving a bushing for the rotating rod, the authors report.**

![Osaka team resolves cryoEM structure of Salmonella P-ring on an elongated flagellar rod](https://realtech.media/media/2026/11/0f894a4971b3d898.jpg)
*Yitzilitt, Wikimedia Commons, CC BY-SA 4.0*

Researchers at the University of Osaka, with Keiichi Namba as senior author, determined the cryoEM structure of the P-ring of the Salmonella flagellar motor assembled on a polyrod, an unusually elongated rod. The study was published in Communications Biology in 2026. The P-ring turned out to be slightly elliptical and tilted by 2.7° relative to the rod axis [1].

The bacterial flagellum enables swimming and consists of more than 30 different proteins. Its LP-ring acts as a bushing around the rod, which serves as a drive shaft, and supports high-speed rotation at low friction. The L-ring, P-ring and distal rod consist of FlgH, FlgI and FlgG, respectively [1].

## Order of LP-ring assembly

The P-ring forms first, around the distal rod, and stays firmly attached to it until the L-ring assembles above it. FlgI monomers form the P-ring. FlgH monomers are translocated to the outer membrane and assemble on the P-ring after the rod grows and penetrates the peptidoglycan layer [1].

In the mature motor the rod rotates inside the LP-ring without physical contact. How the ring is positioned accurately during assembly and how it is later released from the rod had remained unclear, said first author Tomoko Yamaguchi.

## Structure of the assembly intermediate

To capture the intermediate, the team analyzed a polyrod–P-ring complex (PaPR), in which multiple P-rings assemble around genetically modified elongated rods. Single particle cryoEM analysis showed that the elliptical, tilted shape increases the contact area with the rod surface, so the ring binds at a specific position on the rod [1].

In the PaPR the P-ring is tilted by about 3° relative to the rod axis and is slightly elliptical. In the basal body, the matured form, the P-ring is perpendicular to the rod axis and nearly a perfect circle [1].

When the L-ring forms on the tilted P-ring, steric clashes arise between the L-ring and the rod. According to the authors, these clashes detach the P-ring from the rod surface and let it adopt a circular shape, so that the LP-ring becomes a functional bushing around a freely rotating rod [1].

Namba noted that artificially reproducing the autonomous assembly of a complex biomolecular machine remains a major technological challenge, while the bacterial flagellum achieves it through self-organization.

## Sources

1. [Communications Biology](https://doi.org/10.1038/s42003-026-10640-y)
2. [ResearchSEA](https://www.asiaresearchnews.com/node/23657)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-44f578cbc398f28c332cbd02_osaka_team_resolves/