Molecular chaperones in protein folding and translocation

Area of Science:

• Molecular Biology
• Protein Folding
• Cellular Mechanisms

Background:

• Chaperonins like cpn60 and heat shock proteins like hsp70 are crucial for protein homeostasis.
• These molecular chaperones bind and release non-native proteins, assisting in their proper folding and function.
• Understanding their ATPase cycles is key to deciphering cellular protein management.

Purpose of the Study:

• To elucidate the individual steps within the energy-transducing mechanisms of cpn60 and hsp70.
• To provide a detailed picture of how these chaperones influence protein folding, assembly, and translocation.
• To understand the roles of co-proteins (cpn10 and hsp40 family) and nucleotide exchange factors in chaperone function.

Main Methods:

• Detailed biochemical analysis of cpn60 and hsp70 ATPase cycles.
• Investigation of protein-binding dynamics and conformational changes.
• Characterization of the influence of co-proteins and nucleotide exchange factors on chaperone activity.

Main Results:

• The cpn60 reaction cycle involves a cylindrical tetradecamer with a co-protein (cpn10), exhibiting positive and negative cooperativity.
• The hsp70 cycle involves rapid, weak binding of polypeptide segments to the ATP state, triggering hydrolysis and complex stabilization.
• Co-proteins of the hsp40 family enhance, while nucleotide exchange factors destabilize, the hsp70 reaction.

Conclusions:

• The elucidated steps in cpn60 and hsp70 mechanisms offer a refined understanding of chaperone function.
• These chaperones play critical roles in cellular protein folding, assembly, and translocation.
• The asymmetric and alternating cycles of cpn60 and the regulated binding/hydrolysis of hsp70 are vital for cellular proteostasis.