MANF antagonizes nucleotide exchange by the endoplasmic reticulum chaperone BiP

Area of Science:

• Molecular Biology
• Cell Biology
• Neuroscience

Background:

• Mesencephalic astrocyte-derived neurotrophic factor (MANF) is a neuroprotectant.
• MANF is largely retained within the endoplasmic reticulum (ER) of producer cells.
• MANF interacts with the ER-localized Hsp70 chaperone BiP to maintain protein folding homeostasis.

Purpose of the Study:

• To elucidate the mechanism by which MANF interacts with BiP.
• To investigate MANF's role in regulating BiP activity and client release.

Main Methods:

• X-ray crystallography to determine the structure of the MANF SAP domain bound to BiP.
• Biochemical assays to measure ADP release and ATP binding to BiP.
• Cellular assays to assess ER stress responses in MANF-deficient cells.

Main Results:

• The SAP domain of MANF selectively binds to the nucleotide-binding domain (NBD) of ADP-bound BiP.
• MANF stabilizes the ADP-bound conformation of BiP by interacting with specific NBD subdomains.
• MANF inhibits ADP release from and ATP binding to BiP, thereby preventing client protein release.
• MANF-deficient cells exhibit reduced formation of ER stress-induced BiP-containing high molecular weight complexes.

Conclusions:

• MANF functions as a nucleotide exchange inhibitor for BiP.
• MANF stabilizes BiP-client complexes, contributing to protein folding homeostasis in the ER.
• MANF's interaction with BiP is crucial for managing ER stress responses.