A trans-membrane segment inside the ribosome exit tunnel triggers RAMP4 recruitment to the Sec61p translocase

Membrane protein integration occurs predominantly at the endoplasmic reticulum and is mediated by the translocon, which is formed by the Sec61p complex. The translocon binds to the ribosome at the polypeptide exit site such that integration occurs in a cotranslational manner. Ribosomal protein Rpl17 is positioned such that it contacts both the ribosome exit tunnel and the surface of the ribosome near the exit site, where it is intimately associated with the translocon. The presence of a trans-membrane (TM) segment inside the ribosomal exit tunnel leads to the recruitment of RAMP4 to the translocon at a site adjacent to Rpl17. This suggests a signaling function for Rpl17 such that it can recognize a TM segment inside the ribosome and triggers rearrangements of the translocon, priming it for subsequent TM segment integration.

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An ER translocon for multi-pass membrane protein biogenesis

eLife ◽

10.7554/elife.56889 ◽

2020 ◽

Vol 9 ◽

Cited By ~ 7

Author(s):

Philip T McGilvray ◽

S Andrei Anghel ◽

Arunkumar Sundaram ◽

Frank Zhong ◽

Michael J Trnka ◽

...

Keyword(s):

Membrane Proteins ◽

Membrane Protein ◽

Glutamate Transporter ◽

Cell Physiology ◽

Transmembrane Segments ◽

Cryo Electron Microscopy ◽

Protein Biogenesis ◽

Exit Tunnel ◽

Ribosome Exit Tunnel ◽

Molecular Framework

Membrane proteins with multiple transmembrane domains play critical roles in cell physiology, but little is known about the machinery coordinating their biogenesis at the endoplasmic reticulum. Here we describe a ~ 360 kDa ribosome-associated complex comprising the core Sec61 channel and five accessory factors: TMCO1, CCDC47 and the Nicalin-TMEM147-NOMO complex. Cryo-electron microscopy reveals a large assembly at the ribosome exit tunnel organized around a central membrane cavity. Similar to protein-conducting channels that facilitate movement of transmembrane segments, cytosolic and luminal funnels in TMCO1 and TMEM147, respectively, suggest routes into the central membrane cavity. High-throughput mRNA sequencing shows selective translocon engagement with hundreds of different multi-pass membrane proteins. Consistent with a role in multi-pass membrane protein biogenesis, cells lacking different accessory components show reduced levels of one such client, the glutamate transporter EAAT1. These results identify a new human translocon and provide a molecular framework for understanding its role in multi-pass membrane protein biogenesis.

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Faculty Opinions recommendation of Nascent peptide in the ribosome exit tunnel affects functional properties of the A-site of the peptidyl transferase center.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.9313956.9931054 ◽

2011 ◽

Author(s):

Ruben Gonzalez ◽

Daniel MacDougall ◽

Margaret Elvekrog

Keyword(s):

Functional Properties ◽

Peptidyl Transferase ◽

Peptidyl Transferase Center ◽

Nascent Peptide ◽

Exit Tunnel ◽

Ribosome Exit Tunnel ◽

A Site

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Nascent Peptide in the Ribosome Exit Tunnel Affects Functional Properties of the A-Site of the Peptidyl Transferase Center

Molecular Cell ◽

10.1016/j.molcel.2010.12.031 ◽

2011 ◽

Vol 41 (3) ◽

pp. 321-330 ◽

Cited By ~ 84

Author(s):

Haripriya Ramu ◽

Nora Vázquez-Laslop ◽

Dorota Klepacki ◽

Qing Dai ◽

Joseph Piccirilli ◽

...

Keyword(s):

Functional Properties ◽

Peptidyl Transferase ◽

Peptidyl Transferase Center ◽

Nascent Peptide ◽

Exit Tunnel ◽

Ribosome Exit Tunnel ◽

A Site

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TMCC3 localizes at the three-way junctions for the proper tubular network of the endoplasmic reticulum

Biochemical Journal ◽

10.1042/bcj20190359 ◽

2019 ◽

Vol 476 (21) ◽

pp. 3241-3260

Author(s):

Sindhu Wisesa ◽

Yasunori Yamamoto ◽

Toshiaki Sakisaka

Keyword(s):

Endoplasmic Reticulum ◽

Membrane Proteins ◽

Membrane Protein ◽

Mammalian Cells ◽

Coiled Coil ◽

Transmembrane Domains ◽

Domain Family ◽

Coiled Coil Domain ◽

U2os Cells ◽

Er Membrane

The tubular network of the endoplasmic reticulum (ER) is formed by connecting ER tubules through three-way junctions. Two classes of the conserved ER membrane proteins, atlastins and lunapark, have been shown to reside at the three-way junctions so far and be involved in the generation and stabilization of the three-way junctions. In this study, we report TMCC3 (transmembrane and coiled-coil domain family 3), a member of the TEX28 family, as another ER membrane protein that resides at the three-way junctions in mammalian cells. When the TEX28 family members were transfected into U2OS cells, TMCC3 specifically localized at the three-way junctions in the peripheral ER. TMCC3 bound to atlastins through the C-terminal transmembrane domains. A TMCC3 mutant lacking the N-terminal coiled-coil domain abolished localization to the three-way junctions, suggesting that TMCC3 localized independently of binding to atlastins. TMCC3 knockdown caused a decrease in the number of three-way junctions and expansion of ER sheets, leading to a reduction of the tubular ER network in U2OS cells. The TMCC3 knockdown phenotype was partially rescued by the overexpression of atlastin-2, suggesting that TMCC3 knockdown would decrease the activity of atlastins. These results indicate that TMCC3 localizes at the three-way junctions for the proper tubular ER network.

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