Structural transitions modulate the chaperone activities of Grp94.

Area of Science:

• Molecular Biology
• Protein Folding
• Cellular Stress Response

Background:

• Heat shock proteins (Hsp90s) are ATP-dependent chaperones crucial for protein remodeling.
• Grp94, the endoplasmic reticulum (ER) Hsp90 homolog, is essential for folding secretory and membrane proteins.
• The precise collaboration mechanism between Grp94 and the ER Hsp70 chaperone BiP remains unclear.

Purpose of the Study:

• To elucidate the chaperone mechanism of Grp94, focusing on its collaboration with BiP.
• To investigate the role of Grp94's pre-N domain in chaperone activity and client interactions.
• To characterize the structural and functional interplay between Grp94, BiP, and co-chaperones.

Main Methods:

• Integrated in vivo and in vitro functional assays.
• Structural studies to determine Grp94 conformations.
• Analysis of Grp94-client and Grp94-BiP interactions.

Main Results:

• Grp94 directly collaborates with the BiP chaperone system for client folding.
• The pre-N domain of Grp94 suppresses its ATP hydrolysis and active conformation.
• The co-chaperone DnaJB11 promotes Grp94-BiP interaction, activating Grp94's ATPase activity.
• ATP and BiP binding cooperatively induce Grp94's active closed conformation.
• Nucleotide binding reduces Grp94's client affinity, facilitating productive folding.

Conclusions:

• Grp94's chaperone activity is modulated by its pre-N domain and regulated by BiP and DnaJB11.
• The Grp94-BiP collaboration, influenced by nucleotide binding and co-chaperones, is critical for client protein folding.
• Nucleotide-dependent client affinity modulation may represent a conserved mechanism among ER chaperones.