Structure of the Human Signal Peptidase Complex Reveals the Determinants for Signal Peptide Cleavage

Liaci, A. Manuel; Steigenberger, Barbara; Tamara, Sem; Souza, Paulo C. T.; Gröllers-Mulderij, Mariska; Ogrissek, Patrick; Marrink, Siewert J.; Scheltema, Richard A.; Förster, Friedrich

doi:10.1101/2020.11.11.378711

Cited by 6 publications

(8 citation statements)

References 107 publications

(120 reference statements)

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“…Within the arsenal of 'accessory components' employed by the Sec61 complex [9], the signal recognition particle-(SRP) and its ER membrane-localised cognate binding partner, the SRP receptor, constitute the first key players that are encountered by the majority of proteins destined for the secretory pathway. Together, these complexes mediate protein targeting to the ER [4], typically by virtue of an N-terminal hydrophobic stretch of amino acids [13], or signal sequence, that acts as a 'molecular postcode' and, in many cases, is cleaved [11] from the newly synthesised polypeptide once it is committed to membrane translocation and/or insertion.…”

Section: Er Membrane Targeting: the Srpdelivery Systemmentioning

confidence: 99%

“…In contrast to these actively translocated hydrophilic regions of polypeptide, hydrophobic targeting signals are laterally inserted into the lipid bilayer via the lateral gate. In the case of N-terminal signal sequences, they are cleaved from the nascent chain by the signal peptidase complex (SPC) [11] (Fig. 3Aiv) and, ultimately, subject to further processing and/or degradation by signal peptide peptidase [61].…”

Section: Gating Of the Sec61 Complexmentioning

confidence: 99%

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Membrane protein biogenesis at the ER: the highways and byways

2021

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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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Section: Er Membrane Targeting: the Srpdelivery Systemmentioning

confidence: 99%

Section: Gating Of the Sec61 Complexmentioning

confidence: 99%

Membrane protein biogenesis at the ER: the highways and byways

2021

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“…Therefore, structures of ECF transporter complexes embedded in a more native environment are required to understand their interplay with the lipid bilayer. In this context, single-particle analysis by cryogenic electron microscopy (cryo-EM) has shown to be a suitable method to study the role of membrane remodelling with respect to the function of membrane proteins (10)(11)(12)(13)(14)(15)(16)(17). Here, we present the cryo-EM structures of the folate-specific ECF transporter complex (ECF-FolT2) in the inward-facing apo conformation at an overall resolution of 2.7 Å and 3.4 Å, with better To find suitable reconstitution conditions, we varied the amounts of lipids while keeping the ratio of the transport complex to membrane scaffold protein constant, and assessed the quality of the nanodisc reconstitutions by size-exclusion chromatography (SI Appendix, Fig.…”

Section: Introductionmentioning

confidence: 99%

Insights into the bilayer-mediated toppling mechanism of a folate-specific ECF transporter by cryo-EM

Thangaratnarajah

Rheinberger

Slotboom

2021

Proc. Natl. Acad. Sci. U.S.A.

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Energy-coupling factor (ECF)–type transporters are small, asymmetric membrane protein complexes (∼115 kDa) that consist of a membrane-embedded, substrate-binding protein (S component) and a tripartite ATP-hydrolyzing module (ECF module). They import micronutrients into bacterial cells and have been proposed to use a highly unusual transport mechanism, in which the substrate is dragged across the membrane by a toppling motion of the S component. However, it remains unclear how the lipid bilayer could accommodate such a movement. Here, we used cryogenic electron microscopy at 200 kV to determine structures of a folate-specific ECF transporter in lipid nanodiscs and detergent micelles at 2.7- and 3.4-Å resolution, respectively. The structures reveal an irregularly shaped bilayer environment around the membrane-embedded complex and suggest that toppling of the S component is facilitated by protein-induced membrane deformations. In this way, structural remodeling of the lipid bilayer environment is exploited to guide the transport process.

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“…In this case, membrane integration is limited to the lipid moiety of the GPI-anchor [ 90 ]. Cleavable SPs are removed from the inserting or incoming precursor polypeptides by yet another heteromultimeric enzyme, the signal peptidase complex (SPC) [ 91 , 92 ].…”

Section: The Human Sec61 Transloconmentioning

confidence: 99%

Complexity and Specificity of Sec61-Channelopathies: Human Diseases Affecting Gating of the Sec61 Complex

Sicking

Lang

Bochen

et al. 2021

Cells

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The rough endoplasmic reticulum (ER) of nucleated human cells has crucial functions in protein biogenesis, calcium (Ca2+) homeostasis, and signal transduction. Among the roughly one hundred components, which are involved in protein import and protein folding or assembly, two components stand out: The Sec61 complex and BiP. The Sec61 complex in the ER membrane represents the major entry point for precursor polypeptides into the membrane or lumen of the ER and provides a conduit for Ca2+ ions from the ER lumen to the cytosol. The second component, the Hsp70-type molecular chaperone immunoglobulin heavy chain binding protein, short BiP, plays central roles in protein folding and assembly (hence its name), protein import, cellular Ca2+ homeostasis, and various intracellular signal transduction pathways. For the purpose of this review, we focus on these two components, their relevant allosteric effectors and on the question of how their respective functional cycles are linked in order to reconcile the apparently contradictory features of the ER membrane, selective permeability for precursor polypeptides, and impermeability for Ca2+. The key issues are that the Sec61 complex exists in two conformations: An open and a closed state that are in a dynamic equilibrium with each other, and that BiP contributes to its gating in both directions in cooperation with different co-chaperones. While the open Sec61 complex forms an aqueous polypeptide-conducting- and transiently Ca2+-permeable channel, the closed complex is impermeable even to Ca2+. Therefore, we discuss the human hereditary and tumor diseases that are linked to Sec61 channel gating, termed Sec61-channelopathies, as disturbances of selective polypeptide-impermeability and/or aberrant Ca2+-permeability.

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Structure of the Human Signal Peptidase Complex Reveals the Determinants for Signal Peptide Cleavage

Cited by 6 publications

References 107 publications

Membrane protein biogenesis at the ER: the highways and byways

Membrane protein biogenesis at the ER: the highways and byways

Insights into the bilayer-mediated toppling mechanism of a folate-specific ECF transporter by cryo-EM

Complexity and Specificity of Sec61-Channelopathies: Human Diseases Affecting Gating of the Sec61 Complex

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