The bacterial swarming factor SwrD belongs to a diverse family of proteins that form hexameric rings
- 1Cornel University
Abstract
Prokaryotic swarming is a collective surface-associated behavior that supports rapid colonization, biofilm formation, and host interactions. Swarming requires enhanced flagellar motor (FM) torque generation under high-load conditions. In many bacteria, this adaptation is achieved through increased stator unit recruitment and coordinated transcriptional regulation of motility genes. Genetic studies have implicated several relatively poorly characterized proteins in swarming, including SwrD, a component of the fla-che operon whose loss impairs torque generation in Bacillus subtilis. Intriguingly, SwrD is conserved in spirochetes that experience high viscous loads but do not exhibit canonical swarming, suggesting a broader functional role in FM regulation. Here, we structurally and biophysically characterize SwrD from B. subtilis and the spirochete Borrelia burgdorferi. In both cases, we show that SwrD assembles into a hexameric ring-like structure featuring a highly charged, disordered peripheral tail. Whereas SwrD displays structural similarities to periplasmic lipoproteins and DNA-binding proteins, lipidation regions and DNA interaction motifs of these other proteins are not conserved in SwrD. Deletion of swrD in B. subtilis results in pronounced swarming defects and altered expression of fla-che operon transcripts. In silico interaction analyses further identify the stator protein MotA as a high-confidence SwrD interactor, but this interaction could not be validated biochemically. Conserved SwrD residues mediate subunit contacts or locate to the hexamer periphery where they may mediate functionally important interactions.
Related
- A widespread bacterial toxin reveals a deeply divergent DNase family neutralized by diverse immunity proteins.
- The AAA+ superfamily of functionally diverse proteins
- Unbiased and scalable reduction of diverse bacterial genomes
- Diverse stresses converge on bacterial periplasmic expansion through distinct physiological mechanisms
- Diverse signaling proteins recruit RCC1-Like Domain proteins to the plasma membrane through a common structural framework.
BibTeX
@misc{nair2026bacterial,
title = {{The bacterial swarming factor SwrD belongs to a diverse family of proteins that form hexameric rings}},
author = {D. Nair and K. Zhang and A. M. Kahala and C. Li and B. R. CRANE},
howpublished = {bioRxiv},
year = {2026},
month = may,
doi = {10.64898/2026.05.26.727983},
url = {https://www.biorxiv.org/content/10.64898/2026.05.26.727983v2},
note = {CC BY-NC-ND},
}
RIS
TY - UNPB
TI - The bacterial swarming factor SwrD belongs to a diverse family of proteins that form hexameric rings
AU - D. Nair
AU - K. Zhang
AU - A. M. Kahala
AU - C. Li
AU - B. R. CRANE
PY - 2026
DA - 2026/05/26
PB - bioRxiv
DO - 10.64898/2026.05.26.727983
UR - https://www.biorxiv.org/content/10.64898/2026.05.26.727983v2
AB - Prokaryotic swarming is a collective surface-associated behavior that supports rapid colonization, biofilm formation, and host interactions. Swarming requires enhanced flagellar motor (FM) torque generation under high-load conditions. In many bacteria, this adaptation is achieved through increased stator unit recruitment and coordinated transcriptional regulation of motility genes. Genetic studies have implicated several relatively poorly characterized proteins in swarming, including SwrD, a component of the fla-che operon whose loss impairs torque generation in Bacillus subtilis. Intriguingly, SwrD is conserved in spirochetes that experience high viscous loads but do not exhibit canonical swarming, suggesting a broader functional role in FM regulation. Here, we structurally and biophysically characterize SwrD from B. subtilis and the spirochete Borrelia burgdorferi. In both cases, we show that SwrD assembles into a hexameric ring-like structure featuring a highly charged, disordered peripheral tail. Whereas SwrD displays structural similarities to periplasmic lipoproteins and DNA-binding proteins, lipidation regions and DNA interaction motifs of these other proteins are not conserved in SwrD. Deletion of swrD in B. subtilis results in pronounced swarming defects and altered expression of fla-che operon transcripts. In silico interaction analyses further identify the stator protein MotA as a high-confidence SwrD interactor, but this interaction could not be validated biochemically. Conserved SwrD residues mediate subunit contacts or locate to the hexamer periphery where they may mediate functionally important interactions.
ER -