Phosphomimics destabilize Hsp27 oligomeric assemblies and enhance chaperone activity

Area of Science:

• Biochemistry
• Molecular Biology
• Protein Structure

Background:

• Mammalian small heat-shock protein Hsp27's structure and chaperone function are regulated by serine phosphorylation.
• The specific impact of phosphorylation at residues 15, 78, and 82 on Hsp27's oligomeric state and activity remains unclear.

Purpose of the Study:

• To investigate the combinatorial effects of serine phosphorylation mimicry on Hsp27 oligomerization using mass spectrometry.
• To determine the relationship between Hsp27's oligomeric state, phosphorylation, and its chaperone activity.

Main Methods:

• Utilized mass spectrometry to analyze Hsp27 mutants mimicking serine phosphorylation at specific residues.
• Assessed changes in Hsp27 oligomeric state and dissociation propensity.
• Evaluated the impact of these modifications on Hsp27's ability to prevent protein aggregation.

Main Results:

• Hsp27 phosphorylation mimicry, especially triple mutation, significantly decreased average oligomeric size, favoring dimer formation.
• Increased modification correlated with a higher propensity for Hsp27 oligomer dissociation.
• Enhanced chaperone activity, including prevention of amorphous and fibrillar aggregation, was observed and linked to dissociated species.

Conclusions:

• In vivo phosphorylation likely promotes Hsp27 oligomer dissociation, thereby enhancing its chaperone activity.
• The study supports a model where Hsp27 dimers represent the primary chaperone-active component.