Structure of the magnetosome-associated actin-like MamK filament at subnanometer resolution

Area of Science:

• Microbiology
• Structural Biology
• Biophysics

Background:

• Magnetotactic bacteria navigate using intracellular magnetic crystals (magnetosomes).
• Proper magnetosome alignment is crucial for bacterial magnetic sensing and navigation.
• MamK protein filaments are known to anchor magnetosomes within the bacterial cell.

Purpose of the Study:

• To determine the high-resolution structure of the MamK filament.
• To elucidate the molecular basis of MamK filament assembly and architecture.
• To compare MamK structure and contacts with other actin homologs.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was used to obtain the MamK filament structure at approximately 6.5 Å resolution.
• Structural analysis focused on identifying inter-protein contacts and overall filament architecture.

Main Results:

• The MamK filament adopts a double-stranded, non-staggered architecture.
• Longitudinal contacts within each strand resemble eukaryotic actin, while cross-strand contacts are novel.
• The unique cross-strand interface explains the non-staggered filament arrangement.

Conclusions:

• The determined cryo-EM structure reveals the molecular details of MamK filament formation.
• MamK filaments exhibit a unique structural organization distinct from other known actin homologs like MreB.
• This structural insight provides a foundation for understanding magnetosome-cytoskeleton interactions in magnetotactic bacteria.