Basic mechanism of the autonomous ClpG disaggregase.

Area of Science:

• Molecular biology
• Protein biochemistry
• Microbial stress response

Background:

• Bacterial survival under heat stress depends on reactivating aggregated proteins.
• The Hsp70-ClpB system is the primary bacterial disaggregase, requiring Hsp70 for ClpB function.
• Gamma-proteobacteria utilize ClpG as an alternative, autonomous disaggregase.

Purpose of the Study:

• To elucidate the molecular mechanisms underlying ClpG's autonomous disaggregation activity.
• To investigate the roles of ClpG-specific domains and conserved motifs in its function.
• To compare the functional differences between ClpG and the canonical Hsp70-ClpB disaggregase.

Main Methods:

• Analysis of ClpG mutants lacking specific domains.
• Site-directed mutagenesis of conserved motifs in ClpG.
• Assays for protein aggregate binding, ATPase activity, and disaggregation.

Main Results:

• The N-terminal ClpG-specific N1 domain mediates direct binding to protein aggregates.
• Peptide substrate binding overrides repression by N1 and N2 domains, strongly stimulating ClpG ATPase activity.
• Efficient ATPase activity and substrate threading require two functional nucleotide-binding domains.

Conclusions:

• ClpG's autonomous disaggregation activity is primarily mediated by its N1 domain's ability to bind aggregates.
• Substrate availability directly controls ClpG's ATPase and disaggregation functions.
• ClpG represents a distinct evolutionary solution for protein disaggregation compared to the Hsp70-ClpB system.