1
|
Bieniawski MA, Stevens KLP, Witham CM, Steuart RFL, Bankaitis VA, Mousley CJ. Diverse Sphingolipid Species Harbor Different Effects on Ire1 Clustering. Int J Mol Sci 2022; 23:ijms232012130. [PMID: 36293008 PMCID: PMC9602660 DOI: 10.3390/ijms232012130] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2022] [Revised: 09/28/2022] [Accepted: 09/30/2022] [Indexed: 11/16/2022] Open
Abstract
Endoplasmic reticulum (ER) function is dedicated to multiple essential processes in eukaryotes, including the processing of secretory proteins and the biogenesis of most membrane lipids. These roles implicate a heavy burden to the organelle, and it is thus prone to fluctuations in the homeostasis of molecules which govern these processes. The unfolded protein response (UPR) is a general ER stress response tasked with maintaining the ER for optimal function, mediated by the master activator Ire1. Ire1 is an ER transmembrane protein that initiates the UPR, forming characteristic oligomers in response to irregularities in luminal protein folding and in the membrane lipid environment. The role of lipids in regulating the UPR remains relatively obscure; however, recent research has revealed a potent role for sphingolipids in its activity. Here, we identify a major role for the oxysterol-binding protein Kes1, whose activity is of consequence to the sphingolipid profile in cells resulting in an inhibition of UPR activity. Using an mCherry-tagged derivative of Ire1, we observe that this occurs due to inhibition of Ire1 to form oligomers. Furthermore, we identify that a sphingolipid presence is required for Ire1 activity, and that specific sphingolipid profiles are of major consequence to Ire1 function. In addition, we highlight cases where Ire1 oligomerization is absent despite an active UPR, revealing a potential mechanism for UPR induction where Ire1 oligomerization is not necessary. This work provides a basis for the role of sphingolipids in controlling the UPR, where their metabolism harbors a crucial role in regulating its onset.
Collapse
Affiliation(s)
- Mark A. Bieniawski
- Curtin Medical School, Faculty of Health Sciences, Curtin University, Bentley, WA 6102, Australia
- Curtin Health Innovation Research Institute, Faculty of Health Sciences, Curtin University, Bentley, WA 6102, Australia
| | - Kofi L. P. Stevens
- Curtin Medical School, Faculty of Health Sciences, Curtin University, Bentley, WA 6102, Australia
- Curtin Health Innovation Research Institute, Faculty of Health Sciences, Curtin University, Bentley, WA 6102, Australia
| | - Christopher M. Witham
- Curtin Medical School, Faculty of Health Sciences, Curtin University, Bentley, WA 6102, Australia
- Curtin Health Innovation Research Institute, Faculty of Health Sciences, Curtin University, Bentley, WA 6102, Australia
| | - Robert F. L. Steuart
- Curtin Health Innovation Research Institute, Faculty of Health Sciences, Curtin University, Bentley, WA 6102, Australia
| | - Vytas A. Bankaitis
- Department of Molecular and Cellular Medicine, Texas A&M Health Sciences Center, Texas A&M University, College Station, TX 77843-1114, USA
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843-1114, USA
- Department of Chemistry, Texas A&M University, College Station, TX 77843-1114, USA
| | - Carl J. Mousley
- Curtin Medical School, Faculty of Health Sciences, Curtin University, Bentley, WA 6102, Australia
- Curtin Health Innovation Research Institute, Faculty of Health Sciences, Curtin University, Bentley, WA 6102, Australia
- Correspondence:
| |
Collapse
|
2
|
Cancer associated mutations in Sec61γ alter the permeability of the ER translocase. PLoS Genet 2021; 17:e1009780. [PMID: 34460824 PMCID: PMC8439465 DOI: 10.1371/journal.pgen.1009780] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2020] [Revised: 09/14/2021] [Accepted: 08/16/2021] [Indexed: 11/19/2022] Open
Abstract
Translocation of secretory and integral membrane proteins across or into the ER membrane occurs via the Sec61 complex, a heterotrimeric protein complex possessing two essential sub-units, Sec61p/Sec61α and Sss1p/Sec61γ and the non-essential Sbh1p/Sec61β subunit. In addition to forming a protein conducting channel, the Sec61 complex maintains the ER permeability barrier, preventing flow of molecules and ions. Loss of Sec61 integrity is detrimental and implicated in the progression of disease. The Sss1p/Sec61γ C-terminus is juxtaposed to the key gating module of Sec61p/Sec61α and is important for gating the translocon. Inspection of the cancer genome database identifies six mutations in highly conserved amino acids of Sec61γ/Sss1p. We identify that five out of the six mutations identified affect gating of the ER translocon, albeit with varying strength. Together, we find that mutations in Sec61γ that arise in malignant cells result in altered translocon gating dynamics, this offers the potential for the translocon to represent a target in co-therapy for cancer treatment.
Collapse
|
3
|
Bhadra P, Yadhanapudi L, Römisch K, Helms V. How does Sec63 affect the conformation of Sec61 in yeast? PLoS Comput Biol 2021; 17:e1008855. [PMID: 33780447 PMCID: PMC8031780 DOI: 10.1371/journal.pcbi.1008855] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2020] [Revised: 04/08/2021] [Accepted: 03/05/2021] [Indexed: 12/31/2022] Open
Abstract
The Sec complex catalyzes the translocation of proteins of the secretory pathway into the endoplasmic reticulum and the integration of membrane proteins into the endoplasmic reticulum membrane. Some substrate peptides require the presence and involvement of accessory proteins such as Sec63. Recently, a structure of the Sec complex from Saccharomyces cerevisiae, consisting of the Sec61 channel and the Sec62, Sec63, Sec71 and Sec72 proteins was determined by cryo-electron microscopy (cryo-EM). Here, we show by co-precipitation that the Sec61 channel subunit Sbh1 is not required for formation of stable Sec63-Sec61 contacts. Molecular dynamics simulations started from the cryo-EM conformation of Sec61 bound to Sec63 and of unbound Sec61 revealed how Sec63 affects the conformation of Sec61 lateral gate, plug, pore region and pore ring diameter via three intermolecular contact regions. Molecular docking of SRP-dependent vs. SRP-independent signal peptide chains into the Sec61 channel showed that the pore regions affected by presence/absence of Sec63 play a crucial role in positioning the signal anchors of SRP-dependent substrates nearby the lateral gate.
Collapse
Affiliation(s)
- Pratiti Bhadra
- Center for Bioinformatics, Saarland University, Saarbrücken, Saarland, Germany
| | - Lalitha Yadhanapudi
- Faculty of Natural Sciences and Technology, Saarland University, Saarbrücken, Saarland, Germany
| | - Karin Römisch
- Faculty of Natural Sciences and Technology, Saarland University, Saarbrücken, Saarland, Germany
| | - Volkhard Helms
- Center for Bioinformatics, Saarland University, Saarbrücken, Saarland, Germany
| |
Collapse
|