Folding and Insertion of Transmembrane Helices at the ER

Whitley, Paul; Grau, Brayan; Gumbart, James C.; Martínez-Gil, Luis; Mingarro, Ismael

doi:10.3390/ijms222312778

Cited by 14 publications

(7 citation statements)

References 117 publications

(147 reference statements)

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“…The clear reduction in the proportion of N-glycosylated species obtained with chimera 3 compared to chimera 2 ( Figure S4I ) indicates that only a small proportion of HR1 and the appended OPG2 tag are successfully translocated into the ER lumen. This is likely due to a combination of the low proportion of hydrophobic residues and the presence of several charged and polar amino acids in HR1[39]. We thus propose that, for a minority of VPS33b, TMD1 is inserted into the ER membrane as a tail-anchored region with a luminal HR1 that most likely remains associated with the inner leaflet of the bilayer (N-cytosolic, C-luminal; Figure 5A , right).…”

Section: Resultsmentioning

confidence: 99%

Endocytic recycling is central to circadian collagen fibrillogenesis and disrupted in fibrosis

Chang

Pickard

Garva

et al. 2021

Preprint

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Collagen fibrils are the principal supporting elements in vertebrate tissues. They account for 25% of total protein mass, exhibit a broad range of size and organisation depending on tissue and stage of development, and can be under circadian clock control. Here we show that the remarkable dynamic pleomorphism of collagen fibrils is underpinned by a mechanism that distinguishes between collagen secretion and initiation of fibril assembly, at the plasma membrane. Collagen fibrillogenesis occurring at the plasma membrane requires vacuolar protein sorting (VPS) 33b (which is under circadian clock control), collagen-binding integrin-α11 subunit, and is reduced when endocytosis is inhibited. Fibroblasts lacking VPS33b secrete soluble collagen without assembling fibrils, whereas constitutive over-expression of VPS33b increases fibril number with loss of fibril rhythmicity. In conclusion, our study has identified the mechanism that switches secretion of collagen (without forming new fibrils) to new collagen fibril assembly, at the plasma membrane.

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Section: Resultsmentioning

confidence: 99%

Endocytic recycling is central to circadian collagen fibrillogenesis and disrupted in fibrosis

Chang

Pickard

Garva

et al. 2021

Preprint

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“…SPs have a dual function; they target presecretory proteins to the Sec61 complex and trigger the opening of an aqueous channel within the Sec61 complex for translocation of the polypeptide into the ER lumen ( Görlich and Rapoport, 1993 ; Wirth et al, 2003 ; Dejgaard et al, 2010 ; Conti et al, 2015 ; Voorhees and Hegde, 2016 ). TMH are similar to SP in structure and function, except for the positioning of positively charged amino acid residues, which can be up- or downstream of the central hydrophobic region and determine the TMH orientation in the ER membrane, following the “positive inside rule” ( Goder et al, 2004 ; Baker et al, 2017 ; Whitely et al, 2021 ).…”

Section: Introductionmentioning

confidence: 99%

Signal Peptide Features Determining the Substrate Specificities of Targeting and Translocation Components in Human ER Protein Import

et al. 2022

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In human cells, approximately 30% of all polypeptides enter the secretory pathway at the level of the endoplasmic reticulum (ER). This process involves cleavable amino-terminal signal peptides (SPs) or more or less amino-terminal transmembrane helices (TMHs), which serve as targeting determinants, at the level of the precursor polypeptides and a multitude of cytosolic and ER proteins, which facilitate their ER import. Alone or in combination SPs and TMHs guarantee the initial ER targeting as well as the subsequent membrane integration or translocation. Cytosolic SRP and SR, its receptor in the ER membrane, mediate cotranslational targeting of most nascent precursor polypeptide chains to the polypeptide-conducting Sec61 complex in the ER membrane. Alternatively, fully-synthesized precursor polypeptides and certain nascent precursor polypeptides are targeted to the ER membrane by either the PEX-, SND-, or TRC-pathway. Although these targeting pathways may have overlapping functions, the question arises how relevant this is under cellular conditions and which features of SPs and precursor polypeptides determine preference for a certain pathway. Irrespective of their targeting pathway(s), most precursor polypeptides are integrated into or translocated across the ER membrane via the Sec61 channel. For some precursor polypeptides specific Sec61 interaction partners have to support the gating of the channel to the open state, again raising the question why and when this is the case. Recent progress shed light on the client spectrum and specificities of some auxiliary components, including Sec62/Sec63, TRAM1 protein, and TRAP. To address the question which precursors use a certain pathway or component in intact human cells, i.e., under conditions of fast translation rates and molecular crowding, in the presence of competing precursors, different targeting organelles, and relevant stoichiometries of the involved components, siRNA-mediated depletion of single targeting or transport components in HeLa cells was combined with label-free quantitative proteomics and differential protein abundance analysis. Here, we present a summary of the experimental approach as well as the resulting differential protein abundance analyses and discuss their mechanistic implications in light of the available structural data.

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“…Given that the β and γ subunits are not essential to translocation, our simulation systems contain only Sec61α. The hydrophobicity of polypeptide likely controls the open state of the lateral gate; the more hydrophobic, the more dependent on the translocon is the polypeptide . In general belief, the interaction between the hydrophobic polypeptide and the lateral gate induces its opening .…”

Section: Methodsmentioning

confidence: 99%

“…However, some details of the mechanism are still unclear because the whole process of translocation is extremely complex. A recent review paper summarizes the research progress of TMH insertion and folding …”

Section: Introductionmentioning

confidence: 99%

The Pathway of a Transmembrane Helix Insertion into the Membrane Assisted by Sec61α Channel

Gao,

Zhang

2024

Langmuir

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The significant inconsistency between the experimental and simulation results of the free energy for the translocon-assisted insertion of the transmembrane helix (TMH) has not been reasonably explained. Understanding the mechanism of TMH insertion through the translocon is the key to solving this problem. In this study, we performed a series of coarse-grained molecular dynamics simulations and calculated the potential mean forces (PMFs) for three insertion processes of a hydrophobic TMH. The simulations reveal the pathway of the TMH insertion assisted by a translocon. The results indicate that the TMH contacts the top of the lateral gate first and then inserts down the lateral gate, which agrees with the sliding model. The TMH begins to transfer laterally to the bilayer when it is blocked by the plug and reaches the exit of the lateral gate, where there is a free energy minimum point. We also found that the connecting section between TM2 and TM3 of Sec61α prevented TMH from leaving the lateral gate and directly transitioning to the surface-bound state. These findings provide insight into the mechanism of the insertion of TMH through the translocon.

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Folding and Insertion of Transmembrane Helices at the ER

Cited by 14 publications

References 117 publications

Endocytic recycling is central to circadian collagen fibrillogenesis and disrupted in fibrosis

Endocytic recycling is central to circadian collagen fibrillogenesis and disrupted in fibrosis

Signal Peptide Features Determining the Substrate Specificities of Targeting and Translocation Components in Human ER Protein Import

The Pathway of a Transmembrane Helix Insertion into the Membrane Assisted by Sec61α Channel

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