Structural differences in the outer membrane-associated flagellar rings between sheathed and unsheathed flagella

Area of Science:

• Microbiology
• Structural Biology

Background:

• Bacterial flagellar motors are essential for motility.
• Motors exhibit conserved cores but diverse species-specific embellishments.
• Embellishments are categorized as integrated or outer membrane (OM)-associated.

Purpose of the Study:

• To investigate structural variations in flagellar motor embellishments between sheathed and unsheathed flagella.
• To understand the implications of these structural differences for flagellar sheath formation.

Main Methods:

• Cryo-electron tomography was employed to visualize flagellar motor structures.
• Comparative structural analysis was performed across various bacterial species.

Main Results:

• Integrated embellishments of sheathed flagella feature constant-diameter disks and rings.
• Integrated embellishments of unsheathed flagella exhibit variable-diameter components.
• OM-associated embellishments in both types have constant-diameter components, sometimes with an additional extracellular ring.

Conclusions:

• Structural variations in flagellar motor embellishments correlate with flagellar sheath presence.
• The hypothesis proposes that variable-diameter components in unsheathed flagella may hinder OM bending required for sheath formation.