# Hsp40 and Hsp70 in Membrane Protein Triage

> **NIH NIH R01** · UNIV OF NORTH CAROLINA CHAPEL HILL · 2024 · $410,708

## Abstract

Project Summary:
Membrane protein (MP) biogenesis begins in the endoplasmic reticulum (ER) and is a complex process, as
domains on both sides of the ER membrane, and within the membrane bilayer, must fold and assemble. MPs
understudy include ABC-Transporters, P-Type ATPases, G-protein coupled receptors, and BRICHOS proteins.
Missense mutations that cause misfolding and premature degradation of MPs give rise to diseases such as
cystic fibrosis, hypogonadotropic hypogonadism, retinitis pigmentosa and idiopathic lung fibrosis. In order to
prevent toxic accumulation, misfolded MPs are targeted for ER-associated degradation (ERAD) by E3 ubiquitin
ligase complexes. The ER transmembrane Hsp40 DNAJB12 (JB12) recruits cytosolic Hsp70 to the
cytoplasmic face of the ER and together these chaperones deliver the misfolded MPs to ERAD machinery. In
order for a misfolded protein to be a candidate for ERAD however, it must be competent for extraction from the
confines of the ER membrane and delivered to the cytosolic proteasome. Misfolded proteins with structural
restraints that prevent entrance into the proteasome necessitate an alternative quality control mechanism to
ensure degradation. Misfolded MPs expose surfaces in the ER lumen, membrane, and the cytosol, so the
coordinated action of ERQC factors in different locations manage this challenge. Mistakes in MP protein
management are fatal when rogue clients adopt a toxic shape that enable rogues to damage membranes and
dominantly poison essential cell functions. Hsp70 and Hsp40s act with folding and degradation machines to
triage MPs. They shield against proteotoxicity through suppressing aggregation, refolding clients, selection of
clients for degradation and regulating flux though protein biosynthetic systems. A major problem to ERQC
systems are the MPs that accumulate in thermodynamically stable intermediate states that are non-native and
self-associate to form oligomers, amorphous aggregates, and amyloid-like fibrils. Such misfolded conformers
bury surfaces that are normally recognized by ERQC factors, and their thermodynamic stability hinders the
unfolding events required for their extraction from membranes and degradation in the narrow central cavity of
the proteasome. Thermodynamically stable MP intermediates are resistant to ERAD and we discovered that
they are degraded by a JB12 dependent ER-phagy mechanism. The overall goal of the experiments included
in this proposal is to define nodes of cross-talk between the Hsp70 chaperone system, ERAD and ER-phagy
that are essential for cell viability and proteome maintenance.

## Key facts

- **NIH application ID:** 10894119
- **Project number:** 5R01GM151501-02
- **Recipient organization:** UNIV OF NORTH CAROLINA CHAPEL HILL
- **Principal Investigator:** DOUGLAS M CYR
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $410,708
- **Award type:** 5
- **Project period:** 2023-08-01 → 2027-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10894119

## Citation

> US National Institutes of Health, RePORTER application 10894119, Hsp40 and Hsp70 in Membrane Protein Triage (5R01GM151501-02). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10894119. Licensed CC0.

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