Nature Communications· 2026Q1
Structural basis for curvature generation and functional specialization in spirochete flagella
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- 2026year
Short summary
Spirochete flagella generate curvature via asymmetric sheath decoration of a core filament, leading to specialized flagellar architectures that tune motility for diverse pathogenic lifestyles.
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Key points
- Spirochete flagella achieve curvature through asymmetric sheath decoration on a core filament, creating differential axial compaction.
- Two filament types were resolved: FlaB3-only cores and FlaB1/2 cores with a sheath of FlaA and FlaL proteins.
- Sheath asymmetry generates distinct convex and concave filament faces, driving flagellar curvature.
- Sequence and glycosylation differences at sheath-core interfaces allow for regulated filament architecture.
- Conserved FlaL proteins suggest a modular sheath lattice mechanism for tuning flagellar mechanics in diverse spirochetes.
AI-generated from the title and abstract; the full text is not read.
Abstract
Abstract Spirochetes are spiral-shaped bacteria whose curved periplasmic flagella drive corkscrew-like motility through viscous environments. Despite their clinical importance, molecular mechanisms underlying flagellar assembly remain poorly understood. Here, we combine cryo–EM of flagellar filaments natively isolated from oral pathogen Treponema denticola , with proteomics and comparative genomics to characterise the molecular organisation. We resolve two filament types to sub-3 Å resolution: thin FlaB3-only cores, and thick filaments with a FlaB1/2 core asymmetrically decorated by a sheath comprising FlaA1/2/3 and lattice proteins FlaL1/2. We show sheath asymmetry imposes differential axial compaction on the FlaB1/2 core, generating convex and concave filament faces and establishing curvature. FlaB sequence and glycosylation differences at sheath–core interfaces correlate with selective incorporation into distinct filament types, supporting a mechanism for regulated filament architecture. Phylogenetic analysis reveals FlaL conservation across spirochete lineages, suggesting modular sheath lattices provide an adaptable mechanism for tuning flagellar mechanics across diverse pathogenic lifestyles.
The authors' abstract, as published at the source. Nature Communications, 2026 · DOI ↗
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Structural BiologyBiochemistry, Genetics and Molecular Biology