# Biogenesis of multi-pass membrane proteins at the ER

> **NIH NIH R01** · UNIVERSITY OF CHICAGO · 2020 · $319,238

## Abstract

PROJECT SUMMARY
Nearly 30% of the eukaryotic genome encodes integral membrane proteins, which serve many essential
functions as receptors, enzymes, anchors and transporters. Membrane proteins of the cell surface and most
intracellular compartments are first assembled at the endoplasmic reticulum (ER). These proteins are
cotranslationally targeted to the ER by the signal recognition particle and inserted into the bilayer by the Sec61
complex. In the simplest view, the core Sec61 complex mediates insertion by guiding nascent hydrophobic
transmembrane domains (TMDs) into a central, aqueous pore which opens laterally to allow TMD entry into the
bilayer.
 While this model has proven valuable for understanding the basic mechanism of TMD insertion, its
application to the biogenesis of physiologic substrates—especially those with multiple TMDs—has been
challenging. This challenge arises from the extreme diversity of eukaryotic membrane proteins, which have
drastically different topologies and biophysical requirements for insertion, folding, modification and assembly
into functional entities. These different steps are coordinated by the `translocon', a poorly defined and dynamic
ensemble comprising the Sec61 complex in association with a variety of accessory subunits. The structures,
stoichiometry and functions of most of this machinery are poorly understood, and their roles in membrane
protein biogenesis are largely unexplored. Understanding how different translocon complexes mediate
membrane biogenesis is a fundamental question in cell biology
 We recently classified a conserved but poorly understood human protein called TMCO1 as a member
of a previously unrecognized superfamily of proteins involved in membrane protein biogenesis. Consistent with
this assignment, our preliminary data demonstrate that TMCO1 is part of a multi-component assembly that
includes the Sec61 complex and ribosomes, and directly link it to a role in the cotranslational insertion, folding
and/or assembly of a large group of membrane proteins.
 Here we build on this conceptual and technical foundation to define how TMCO1 functions in
membrane protein biogenesis. In Aim 1, we will globally identify the set of nascent TMCO1 substrates and use
these to define the mechanism of TMCO1 action. In Aim 2, we will rigorously analyze the interaction partners
of TMCO1 and define the structure of TMCO1-containing ribosome-Sec61 complexes. We will do this using a
multi-disciplinary approach that combines biochemical, genetic and structural analyses.

## Key facts

- **NIH application ID:** 9954096
- **Project number:** 5R01GM130051-03
- **Recipient organization:** UNIVERSITY OF CHICAGO
- **Principal Investigator:** Robert J Keenan
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $319,238
- **Award type:** 5
- **Project period:** 2018-07-01 → 2022-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9954096

## Citation

> US National Institutes of Health, RePORTER application 9954096, Biogenesis of multi-pass membrane proteins at the ER (5R01GM130051-03). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/9954096. Licensed CC0.

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