Molecular Mechanisms of SURF4- mediated Protein Secretion
type: CreativeWork
description: Protein secretion is an essential process that drives organelle biogenesis, cell growth and communication. Once synthesised and processed in the Endoplasmic Reticulum (ER), secretory proteins are incorporated into transport carriers that are generated by the COPII coat. Efficient and accurate cargo incorporation into ER-derived carriers is driven by transmembrane cargo receptors. ER export receptors are especially important for secretion of soluble cargo as they provide a transmembrane bridge to the cytosolic COPII coat. This study focused on SURF4, a cargo receptor for soluble cargo. I characterised the spectrum of SURF4 clients in HEK-293TREx and Huh7 cells using mass spectrometry. Amongst the top hits, I identified many oligomeric Ca2+-binding proteins, including Cab45 and NUCB1. Using *in vitro* translation and sitespecific photo-crosslinking, I showed direct co-translational SURF4 engagement with the cargo via an N-terminal ER-ESCAPE motif, exposed after signal peptide cleavage. This result supports a fast-export mechanism for preventing improper cargo oligomerization in an early organelle, and for the first time shows a cargo receptor can interact with an unfolded and incompletely translated client. Furthermore, with the aid of structural prediction-guided mutagenesis and site-specific cross-linking, I mapped a putative ER-ESCAPE interaction surface on SURF4 to an ER lumen-facing pocket. Additionally, my work examined SURF4 interactions with the COPII cargo adaptor, SEC24. Whereas Cab45 and NUCB1 use SEC24C/D isoforms, a previously described SURF4 cargo, PCSK9, which exposes ER-ESCAPE after propeptide autocleavage, exclusively employs SEC24A. I show that this discrepancy is due to a PCSK9 requirement for a co-receptor, TMED10. Using a protein-protein interaction assay and various SEC24 and SURF4 binding mutants, I showed that SURF4 uses C-terminal hydrophobic and acidic amino acids to bind the B-site on SEC24C. Conversely, SEC24A recognises a cytosolic loop on…
abstract: Protein secretion is an essential process that drives organelle biogenesis, cell growth and communication. Once synthesised and processed in the Endoplasmic Reticulum (ER), secretory proteins are incorporated into transport carriers that are generated by the COPII coat. Efficient and accurate cargo incorporation into ER-derived carriers is driven by transmembrane cargo receptors. ER export receptors are especially important for secretion of soluble cargo as they provide a transmembrane bridge to the cytosolic COPII coat. This study focused on SURF4, a cargo receptor for soluble cargo. I characterised the spectrum of SURF4 clients in HEK-293TREx and Huh7 cells using mass spectrometry. Amongst the top hits, I identified many oligomeric Ca2+-binding proteins, including Cab45 and NUCB1. Using *in vitro* translation and sitespecific photo-crosslinking, I showed direct co-translational SURF4 engagement with the cargo via an N-terminal ER-ESCAPE motif, exposed after signal peptide cleavage. This result supports a fast-export mechanism for preventing improper cargo oligomerization in an early organelle, and for the first time shows a cargo receptor can interact with an unfolded and incompletely translated client. Furthermore, with the aid of structural prediction-guided mutagenesis and site-specific cross-linking, I mapped a putative ER-ESCAPE interaction surface on SURF4 to an ER lumen-facing pocket. Additionally, my work examined SURF4 interactions with the COPII cargo adaptor, SEC24. Whereas Cab45 and NUCB1 use SEC24C/D isoforms, a previously described SURF4 cargo, PCSK9, which exposes ER-ESCAPE after propeptide autocleavage, exclusively employs SEC24A. I show that this discrepancy is due to a PCSK9 requirement for a co-receptor, TMED10. Using a protein-protein interaction assay and various SEC24 and SURF4 binding mutants, I showed that SURF4 uses C-terminal hydrophobic and acidic amino acids to bind the B-site on SEC24C. Conversely, SEC24A recognises a cytosolic loop on…
author: Maldutyte, Julija
language: eng
keywords: COPII, Membrane terafficking, Protein secretion, SURF4
license: https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/52f6c2f4-56d0-4118-b4d0-e8cab000c85e/download
license: https://www.rioxx.net/licenses/all-rights-reserved/
date published: 2023-06-30
date modified: 2026-07-22T22:24:00Z
provider: Cambridge University
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Cambridge

PropertyValue
property ID: DOI
value: 10.17863/CAM.104368