Asymmetric sheath coordination controls flagellar architecture and function in Leptospira spirochete

Area of Science:

• Microbiology
• Molecular Biology
• Biophysics

Background:

• Bacterial flagella are crucial for motility, with diverse structures and mechanisms.
• Spirochetes uniquely employ periplasmic flagella (PFs) that cause cell body distortion for movement.

Purpose of the Study:

• To elucidate the assembly, curvature, and rigidity mechanisms of periplasmic flagella (PFs) in Leptospira biflexa.
• To understand the cooperative interactions among PF sheath proteins and their role in motility.

Main Methods:

• Generated sheath protein knockout mutants of Leptospira biflexa.
• Utilized high-resolution cryo-electron microscopy to analyze PF structure and assembly.

Main Results:

• The PF comprises a FlaB1 core filament asymmetrically surrounded by sheath proteins.
• Specific proteins (FlaA2, FcpA, FcpB) mediate core-sheath interactions, inducing curvature and rigidity.
• Glycosylation of FlaB1 appears to guide sheath component assembly and interactions.

Conclusions:

• Cooperative interactions among periplasmic flagella sheath proteins confer structural and mechanical specialization.
• Proposed model: transient sheath protein interaction with the core, anchored to the outer membrane, allows core rotation for motility.