Structural rearrangements enable precise positioning, release, and low-friction rotation

Osaka. Japan - The bacterial flagellum is a motility organelle that enables bacteria to swim and is composed of more than 30 different proteins. Researchers have long sought to understand how this complex nanomachine self-assembles from many parts in the correct order and at the correct positions. In a study published in Communications Biology, a research team at the University of Osaka revealed the mechanism by which the flagellar motor assembles its bushing around the drive shaft.

The LP-ring acts as a molecular bushing surrounding the drive shaft called the rod and supports high-speed rotation of the rod at low friction. During motor assembly, the rod first polymerizes, after which the P-ring forms around a specific part of the rod. The L-ring subsequently assembles on top of the P-ring, and the completed LP-ring is released from the rod surface to become a bushing.

“Because the rod rotates within the mature LP-ring without physical contact, it has long been unclear how the LP-ring is accurately positioned during assembly and how it is later released from the rod,” says Tomoko Yamaguchi. “To understand how the LP-ring assembles, we needed structural information on the assembly intermediate. “

To capture the assembly intermediate, the researchers analyzed a polyrod–P-ring complex (PaPR), in which multiple P-rings assemble around genetically-modified elongated rods. Using electron cryomicroscopy (cryoEM) single particle analysis, they found that the P-ring initially adopts a slightly elliptical and tilted conformation to increase the contact area with the rod surface to bind to a specific position of the rod. Then, upon formation of the L-ring, steric hindrance arises between the rod and the L-ring, causing the entire LP-ring to detach from the rod surface and become a functional bushing.

“Artificially reproducing the autonomous assembly of a complex biomolecular machine remains major technological challenge,” says the senior author Keiichi Namba. “The bacterial flagellum achieves this process with remarkable precision through self-organization.”

The newly identified mechanism for constructing and releasing a molecular bearing provides important design principles for self-assembling nanomachines and could contribute to future nanotechnology applications, including highly efficient drug delivery systems (DDSs).
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The article, “Structural insights into the assembly mechanism of the molecular bushing in the bacterial flagellar motor,” was published in Communications Biology at DOI: https://doi.org/10.1038/s42003-026-10640-y

About The University of Osaka
The University of Osaka was founded in 1931 as one of the seven imperial universities of Japan and is now one of Japan's leading comprehensive universities with a broad disciplinary spectrum. This strength is coupled with a singular drive for innovation that extends throughout the scientific process, from fundamental research to the creation of applied technology with positive economic impacts. Its commitment to innovation has been recognized in Japan and around the world. Now, The University of Osaka is leveraging its role as a Designated National University Corporation selected by the Ministry of Education, Culture, Sports, Science and Technology to contribute to innovation for human welfare, sustainable development of society, and social transformation.
Website: https://resou.osaka-u.ac.jp/en