# Demystifying the interaction of UGGT, the ER folding gatekeeper, with its substrates and co-chaperone

> **NIH NIH F32** · UNIVERSITY OF MASSACHUSETTS AMHERST · 2024 · $74,284

## Abstract

Demystifying the interaction of UGGT, the ER folding gatekeeper, with its substrates and co-
chaperone
Project Abstract
Proteins must fold into specific 3-dimensional structures to attain their function, but this process can be
error prone. Worse yet, accumulation of misfolded proteins can lead to diseases such as Alzheimer’s and
Parkinson’s. To mitigate this risk, nature has evolved sophisticated mechanisms to assist protein folding
and assess their folding status. One such example is the endoplasmic reticulum protein quality control
(ERQC) cycle, where the enzyme UDP-glucose: glycoprotein glucosyltransferase (UGGT) serves as the
master regulator. UGGT can sense the folding status of its clients and selectively adds a glucose residue
to the N-glycans of non-natively folded proteins. Substrates modified by UGGT are retained within the
ERQC cycle for further attempts at productive folding. Prior studies have determined that UGGT prefers
“near-native” substrates that present molten-globule conformations. Nonetheless, a structural description
of the folding-sensing mechanism of UGGT remains unknown. UGGT can act alone, but also forms a
complex with a co-chaperone, the 15-kDa selenoprotein (SEP15). This protein contains a redox-active
selenocysteine residue and is thought to aid UGGT in QC of disulfide-rich substrates, but few structural
and functional studies have been performed. This project will utilize a combination of cellular and
biophysical experiments to investigate the interactions of UGGT with its substrates and co-chaperones.
First, structural studies of UGGT and the UGGT/SEP15 complex are underway. These results will provide
insights into the concerted action of UGGT and SEP15. In parallel, endogenous substrates of
UGGT/Sep15 will be identified in mammalian cell culture using a glycoproteomics assay and their
maturation characterized. Second, UGGT-substrate interactions will be investigated using the disease-
causing null Hong Kong variant of ɑ1-antitrypsin as a model substrate. Specific UGGT residues involved
in client recognition will be identified using photo-crosslinking mass spectrometry (XL-MS) experiments.
This work will be performed under the guidance of two leaders in the field of protein homeostasis. Dr. Lila
Gierasch is a leader in the field of protein chaperone biophysics, while Dr. Daniel Hebert is an expert in
the cell biology of glycoprotein quality control. This project will leverage my background in analytical
chemistry and provide critical training in biochemistry and cell biology. Additionally, I will become well-
versed in the broader field of protein homeostasis (proteostasis). After completing the training described
in this proposal, I will be ready to launch my independent academic career studying the structural biology
of ER proteostasis.

## Key facts

- **NIH application ID:** 10996959
- **Project number:** 1F32GM156016-01
- **Recipient organization:** UNIVERSITY OF MASSACHUSETTS AMHERST
- **Principal Investigator:** Robert V Williams
- **Activity code:** F32 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $74,284
- **Award type:** 1
- **Project period:** 2024-09-01 → 2025-08-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10996959

## Citation

> US National Institutes of Health, RePORTER application 10996959, Demystifying the interaction of UGGT, the ER folding gatekeeper, with its substrates and co-chaperone (1F32GM156016-01). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10996959. Licensed CC0.

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