Membrane translocation at the ER: with a little help from my friends

O’Keefe, Sarah; High, Stephen

doi:10.1111/febs.15309

Cited by 13 publications

(19 citation statements)

References 18 publications

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“…This could mean that the cleaved cargo is passed to one or more intermediate factors post plasmepsin V cleavage before being taken by HSP101, or alternatively, HSP101 competes with plasmepsin V for cargo binding. A alternative explanation could also be proposed, where HSP101 binds to cargo prior to plasmepsin V cleavage, perhaps through interaction with the ER import translocon [23, 56], and releases it momentarily for plasmepsin V to cleave the PEXEL motif before immediately resuming its interaction with the mature cargo.…”

Section: Discussionmentioning

confidence: 99%

A revised mechanism for how Plasmodium falciparum recruits and exports proteins into its erythrocytic host cell

Gabriela

Matthews

Boshoven

et al. 2021

Preprint

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Plasmodium falciparum exports ~10% of its proteome into its host erythrocyte to modify the host cell’s physiology. The Plasmodium export element (PEXEL) motif contained within the N-terminus of most exported proteins directs the trafficking of those proteins into the erythrocyte. To reach the host cell, the PEXEL motif of exported proteins are processed by the endoplasmic reticulum (ER) resident aspartyl protease plasmepsin V. Then, following secretion into the parasite-encasing parasitophorous vacuole, the mature exported protein must be unfolded and translocated across the parasitophorous vacuole membrane by the Plasmodium translocon of exported proteins (PTEX). PTEX is a protein-conducting channel consisting of the pore-forming protein EXP2, the protein unfoldase HSP101, and structural component PTEX150. The mechanism of how exported proteins are specifically trafficked from the parasite’s ER following PEXEL cleavage to PTEX complexes on the parasitophorous vacuole membrane is currently not understood. Here, we present evidence that EXP2 and PTEX150 form a stable subcomplex that facilitates HSP101 docking. We also demonstrate that HSP101 localises both within the parasitophorous vacuole and within the parasite’s ER throughout the ring and trophozoite stage of the parasite, coinciding with the timeframe of protein export. Interestingly, we found that HSP101 can form specific interactions with model PEXEL proteins in the parasite ER, irrespective of their PEXEL processing status. Collectively, our data suggest that HSP101 recognises and chaperones PEXEL proteins from the ER to the parasitophorous vacuole and given HSP101’s specificity for the EXP2-PTEX150 subcomplex, this provides a mechanism for how exported proteins are specifically targeted to PTEX for translocation into the erythrocyte.

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Section: Discussionmentioning

confidence: 99%

A revised mechanism for how Plasmodium falciparum recruits and exports proteins into its erythrocytic host cell

Gabriela

Matthews

Boshoven

et al. 2021

Preprint

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“…Once substrates with special requirements start the gating process, Sec61β allows rapid integration of Sec63 into the active translocon. If so, Sec61β and Sec63 eventually will show a partially overlapping substrate-spectrum, which remains to be seen [ 6 , 18 , 67 ]. This scenario is reminiscent of a previous report showing the recruitment of the signal peptidase complex to the active, ribosome-engaged translocon by Sec61β [ 68 ].…”

Section: Discussionmentioning

confidence: 99%

“…One of the organelles that supports both intracellular signaling, for example calcium (Ca 2+ ) signaling or the unfolded protein response, and secretion of proteohormones is the endoplasmic reticulum (ER) [ 1 , 2 , 3 , 4 ]. A major membrane protein at the crossroad of ER signaling and protein transport is the heterotrimeric Sec61 complex acting as the pore-forming component of the ER protein translocase [ 5 , 6 , 7 ].…”

Section: Introductionmentioning

confidence: 99%

Lights, Camera, Interaction: Studying Protein–Protein Interactions of the ER Protein Translocase in Living Cells

Sicking

Jung

Lang

2021

IJMS

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Various landmark studies have revealed structures and functions of the Sec61/SecY complex in all domains of live demonstrating the conserved nature of this ancestral protein translocase. While the bacterial homolog of the Sec61 complex resides in the plasma membrane, the eukaryotic counterpart manages the transfer of precursor proteins into or across the membrane of the endoplasmic reticulum (ER). Sec61 complexes are accompanied by a set of dynamically recruited auxiliary proteins assisting the transport of certain precursor polypeptides. TRAP and Sec62/Sec63 are two auxiliary protein complexes in mammalian cells that have been characterized by structural and biochemical methods. Using these ER membrane protein complexes for our proof-of-concept study, we aimed to detect interactions of membrane proteins in living mammalian cells under physiological conditions. Bimolecular luminescence complementation and competition was used to demonstrate multiple protein–protein interactions of different topological layouts. In addition to the interaction of the soluble catalytic and regulatory subunits of the cytosolic protein kinase A, we detected interactions of ER membrane proteins that either belong to the same multimeric protein complex (intra-complex interactions: Sec61α–Sec61β, TRAPα–TRAPβ) or protein complexes in juxtaposition (inter-complex interactions: Sec61α–TRAPα, Sec61α–Sec63, and Sec61β–Sec63). In the process, we established further control elements like synthetic peptide complementation for expression profiling of fusion constructs and protease-mediated reporter degradation demonstrating the cytosolic localization of a reporter complementation. Ease of use and flexibility of the approach presented here will spur further research regarding the dynamics of protein–protein interactions in response to changing cellular conditions in living cells.

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“…However, there is now a growing body of evidence that signal sequences can provide an additional, as yet poorly defined, level of control during membrane translocation [62]. Highly diverse in terms of their hydrophobicity, length, charge and specific amino acid composition [8,13,63], ER targeting signals appear to regulate the opening, or 'gating' of the Sec61 translocon [62], particularly since SRP effectively caters for targeting signals seemingly irrespective of their intrinsic ability to gate the translocon which, in some cases, is 'inefficient' and 'slow' (Fig. 3C) [64,65].…”

Section: Gating Of the Sec61 Complexmentioning

confidence: 99%

“…Furthermore, given that different gating assistants can contribute to the efficient translocation of the same protein substrate, whether a secretory protein or TMP (Fig. 3Ei, Tables 1-4) [74], and cellular levels of TRAP-b are upregulated following depletion of Sec62 [74], it seems likely that the TRAP complex and Sec62/Sec63 perform overlapping, but nonidentical, functions during Sec61-mediated protein translocation [62].…”

Section: Gating Of the Sec61 Complexmentioning

confidence: 99%

Membrane protein biogenesis at the ER: the highways and byways

2021

Self Cite

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The Sec61 complex is the major protein translocation channel of the endoplasmic reticulum (ER), where it plays a central role in the biogenesis of membrane and secretory proteins. Whilst Sec61-mediated protein translocation is typically coupled to polypeptide synthesis, suggestive of significant complexity, an obvious characteristic of this core translocation machinery is its surprising simplicity. Over thirty years after its initial discovery, we now understand that the Sec61 complex is in fact the central piece of an elaborate jigsaw puzzle, which can be partly solved using new research findings. We propose that the Sec61 complex acts as a dynamic hub for cotranslational protein translocation at the ER, proactively recruiting a range of accessory complexes that enhance and regulate its function in response to different protein clients. It is now clear that the Sec61 complex does not have a monopoly on co-translational insertion, with some transmembrane proteins preferentially utilising the ER membrane complex instead. We also have a better understanding of post-insertion events, where at least one membrane-embedded chaperone complex can capture the newly inserted transmembrane domains of multi-span proteins and co-ordinate their assembly into a native structure. Having discovered this array of Sec61-associated components and competitors, our next challenge is to understand how they act together in order to expand the range and complexity of the membrane proteins that can be synthesised at the ER. Furthermore, this diversity of components and pathways may open up new opportunities for targeted therapeutic interventions designed to selectively modulate protein biogenesis at the ER. AbbreviationsBiP, immunoglobulin binding protein; CCDC47, coiled-coil domain containing 47 protein, also known as calumin; EMC, ER membrane complex; ER, endoplasmic reticulum; GET, guided entry of tail-anchored proteins; hSnd2, human SRP-independent protein 2, also known as TMEM208; NAC, nascent polypeptide-associated complex; NOMO, nodal modulating protein; PAT, protein associated with the ER translocon; RNC, ribosome-nascent chain; SGTA, small glutamine-rich tetratricopeptide repeat-containing protein alpha; SND, SRPindependent proteins or pathway; SPC, signal peptidase complex; SRP, signal recognition particle; TA, tail-anchored; TMCO1, transmembrane and coiled-coil domains 1 protein; TMD, transmembrane domain; TMEM147, transmembrane protein 147; TMEM208, transmembrane protein 208; TMP, transmembrane protein; TRAM, translocating chain-associated membrane protein; TRAP, transloconassociated protein; TRC40, transmembrane recognition complex of 40 kDa, also known as Asna1.

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Membrane translocation at the ER: with a little help from my friends

Cited by 13 publications

References 18 publications

A revised mechanism for how Plasmodium falciparum recruits and exports proteins into its erythrocytic host cell

A revised mechanism for how Plasmodium falciparum recruits and exports proteins into its erythrocytic host cell

Lights, Camera, Interaction: Studying Protein–Protein Interactions of the ER Protein Translocase in Living Cells

Membrane protein biogenesis at the ER: the highways and byways

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