Chaperonin filaments: the archaeal cytoskeleton?

Area of Science:

• Biochemistry
• Cell Biology
• Archaea Research

Background:

• Chaperonins are vital protein-folding proteins found in all domains of life.
• In hyperthermophilic archaea like Sulfolobus shibatae, chaperonins constitute a significant portion of cellular protein.
• High intracellular concentrations suggest potential non-canonical functions beyond protein folding.

Purpose of the Study:

• To investigate the in vivo existence and potential function of chaperonin filaments in Sulfolobus shibatae.
• To determine the conditions under which purified chaperonins form filaments.
• To explore the possible cytoskeletal role of chaperonin filaments in archaea.

Main Methods:

• Purification of chaperonins from Sulfolobus shibatae.
• In vitro filament formation assays with purified chaperonins, Mg2+, and nucleotides.
• Electron microscopy of unfixed, stained S. shibatae cells.
• ImmunoGold labeling using chaperonin-specific antibodies.

Main Results:

• Purified chaperonins form filaments at physiological temperatures in the presence of Mg2+ and nucleotides, requiring nucleotide binding but not hydrolysis.
• Filamentous structures resembling in vitro formed chaperonin filaments were observed in S. shibatae cells.
• ImmunoGold labeling revealed chaperonins associated with insoluble cellular structures, some appearing filamentous.

Conclusions:

• Chaperonin filaments likely exist in vivo in Sulfolobus shibatae, potentially forming an extensive cytostructure.
• The formation of chaperonin filaments suggests a regulatory mechanism for protein-folding activity.
• Chaperonin filaments may serve a cytoskeletal role in archaeal cells.