# Protein quality control at eukaryotic membranes.

> **NIH NIH R35** · UNIVERSITY OF MICHIGAN AT ANN ARBOR · 2021 · $378,492

## Abstract

Endoplasmic reticulum-associated degradation (ERAD) is a process in which ER proteins are degraded, either
because they are misfolded or because their degradation is physiologically regulated. The hallmark substrate of
this process is HMG-CoA reductase, an enzyme catalyzing the rate-limiting step in cholesterol synthesis. In
addition to degrading metabolically-regulated or misfolded proteins, ERAD functions as stress-response system
to alleviate ER stress. While its normal function is to target misfolded or regulated proteins, ERAD is also
exploited by bacterial and viral pathogens to gain access to the cytosol. During normal ERAD, protein substrates
are selected within the ER lumen, moved across the membrane to the cytosol (retrotranslocation), where they
are polyubiquitinated, extracted from the membrane and degraded by the proteasome. How physiologically-
regulated substrates are selected for degradation and the specific cellular pathways under the control of ERAD
are ambiguous. Recent work has demonstrated that a central, conserved ubiquitin ligase called Hrd1, forms a
ubiquitin-gated protein-conducting channel that that is sufficient to allow retrotranslocation of misfolded lumenal
and integral membrane proteins. The autoubiquitination-gating mechanism presents a conundrum; under normal
circumstances, ubiquitination will result in degradation of the modified protein. However, Hrd1 is relatively stable
meaning there are unidentified mechanisms in place to protect autoubiquitinated Hrd1 from degradation and to
reverse the ubiquitin-gated activation. Along with the regulation of Hrd1, many associated processes including
substrate selection by ERAD are mysterious. The goals of this proposal are to 1) define how the ERAD system
is regulated, 2) determine how the ERAD system recognizes its targets, 3) define the features of targets directing
them to ERAD (the degrons), 4) understand how the membrane contributes to ERAD function, and 5) identify
the cellular function of other (non-ERAD) integral membrane protein quality control systems. We will use a
multifaceted approach with biochemistry, cell biology, genetics, and proteomics to address these central
questions in membrane-associated protein quality control. We will leverage our unique in vivo and in vitro assays
(and continue to design innovative assays) to dissect the basic mechanisms of these eukaryotic systems. A
mechanistic understanding of how the systems function (including ERAD) and the processes they regulate will
establish these systems as viable therapeutic targets in medically relevant pathways of protein misfolding,
protein misregulation, and pathogen hijacking.

## Key facts

- **NIH application ID:** 10224814
- **Project number:** 5R35GM128592-04
- **Recipient organization:** UNIVERSITY OF MICHIGAN AT ANN ARBOR
- **Principal Investigator:** Ryan Douglas Baldridge
- **Activity code:** R35 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $378,492
- **Award type:** 5
- **Project period:** 2018-08-15 → 2023-07-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10224814

## Citation

> US National Institutes of Health, RePORTER application 10224814, Protein quality control at eukaryotic membranes. (5R35GM128592-04). Retrieved via AI Analytics 2026-05-25 from https://api.ai-analytics.org/grant/nih/10224814. Licensed CC0.

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