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Abstract The flagellar motor is a powerful macromolecular machine used to propel bacteria through various environments. We determined that flagellar motility of the alpha‐proteobacteriumSinorhizobium melilotiis nearly abolished in the absence of the transcriptional regulator LdtR, known to influence peptidoglycan remodeling and stress response. LdtR does not regulate motility gene transcription. Remarkably, the motility defects of the ΔldtRmutant can be restored by secondary mutations in the motility genemotAor a previously uncharacterized gene in the flagellar regulon, which we namedmotS. MotS is not essential forS. melilotimotility and may serve an accessory role in flagellar motor function. Structural modeling predicts that MotS comprised an N‐terminal transmembrane segment, a long‐disordered region, and a conserved β‐sandwich domain. The C terminus of MotS is localized in the periplasm. Genetics based substitution of MotA with MotAG12Salso restored the ΔldtRmotility defect. The MotAG12Svariant protein features a local polarity shift at the periphery of the MotAB stator units. We propose that MotS may be required for optimal alignment of stators in wild‐type flagellar motors but becomes detrimental in cells with altered peptidoglycan. Similarly, the polarity shift in stator units composed of MotB/MotAG12Smight stabilize its interaction with altered peptidoglycan.
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This content will become publicly available on March 14, 2026
Evolutionary adaptations of doublet microtubules in trypanosomatid parasites
The movement and pathogenicity of trypanosomatid species, the causative agents of trypanosomiasis and leishmaniasis, are dependent on a flagellum that contains an axoneme of dynein-bound doublet microtubules (DMTs). In this work, we present cryo–electron microscopy structures of DMTs from two trypanosomatid species,Leishmania tarentolae and Crithidia fasciculata, at resolutions up to 2.7 angstrom. The structures revealed 27 trypanosomatid-specific microtubule inner proteins, a specialized dynein-docking complex, and the presence of paralogous proteins that enable higher-order periodicities or proximal-distal patterning. Leveraging the genetic tractability of trypanosomatid species, we quantified the location and contribution of each structure-identified protein to swimming behavior. Our study shows that proper B-tubule closure is critical for flagellar motility, exemplifying how integrating structural identification with systematic gene deletion can dissect individual protein contributions to flagellar motility.
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- Award ID(s):
- 2434879
- PAR ID:
- 10583159
- Publisher / Repository:
- AAAS
- Date Published:
- Journal Name:
- Science
- Volume:
- 387
- Issue:
- 6739
- ISSN:
- 0036-8075
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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