Core-sheath coupling controls flagellar curvature and motility in Leptospira

Area of Science:

• Microbiology
• Structural Biology
• Biophysics

Background:

• Spirochete pathogens, including those causing syphilis, Lyme disease, and leptospirosis, are highly invasive.
• Their tissue penetration relies on periplasmic flagellar filaments encased in a unique multi-protein sheath, deforming the cell body into motile waves.
• The mechanical properties enabling this invasive motility remain poorly understood.

Purpose of the Study:

• To determine the atomic structures of the Leptospira endoflagellar filament.
• To elucidate the relationship between filament structure and invasive motility.
• To investigate the role of flagellin variants and sheath composition in motility.

Main Methods:

• Atomic structure determination of the Leptospira endoflagellar filament.
• Analysis of flagellin variants and their influence on sheath composition.
• Measurement of filament curvature and motility in viscous environments and during infection.

Main Results:

• Complete atomic structures of the Leptospira endoflagellar filament were determined.
• The filament sheath comprises 9 to 12 distinct, asymmetrically arranged proteins.
• Flagellin variants dictate sheath composition, yielding curvatures from ~3.5 µm⁻¹ to ~5 µm⁻¹.
• Lower-curvature architecture is crucial for pathogenic Leptospira interrogans' motility in viscous environments and infection.

Conclusions:

• Leptospira achieves environment-specific motility via modular core-sheath coupling.
• This mechanism links atomic-scale structural plasticity to macroscopic swimming behavior.
• Conservation of sheath components suggests this motility mechanism may be widespread among spirochetes.