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Tirincsi A, Sicking M, Hadzibeganovic D, Haßdenteufel S, Lang S. The Molecular Biodiversity of Protein Targeting and Protein Transport Related to the Endoplasmic Reticulum. Int J Mol Sci 2021; 23:143. [PMID: 35008565 PMCID: PMC8745461 DOI: 10.3390/ijms23010143] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2021] [Revised: 12/19/2021] [Accepted: 12/20/2021] [Indexed: 12/15/2022] Open
Abstract
Looking at the variety of the thousands of different polypeptides that have been focused on in the research on the endoplasmic reticulum from the last five decades taught us one humble lesson: no one size fits all. Cells use an impressive array of components to enable the safe transport of protein cargo from the cytosolic ribosomes to the endoplasmic reticulum. Safety during the transit is warranted by the interplay of cytosolic chaperones, membrane receptors, and protein translocases that together form functional networks and serve as protein targeting and translocation routes. While two targeting routes to the endoplasmic reticulum, SRP (signal recognition particle) and GET (guided entry of tail-anchored proteins), prefer targeting determinants at the N- and C-terminus of the cargo polypeptide, respectively, the recently discovered SND (SRP-independent) route seems to preferentially cater for cargos with non-generic targeting signals that are less hydrophobic or more distant from the termini. With an emphasis on targeting routes and protein translocases, we will discuss those functional networks that drive efficient protein topogenesis and shed light on their redundant and dynamic nature in health and disease.
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Affiliation(s)
- Andrea Tirincsi
- Department of Medical Biochemistry and Molecular Biology, Saarland University, 66421 Homburg, Germany; (A.T.); (M.S.); (D.H.)
| | - Mark Sicking
- Department of Medical Biochemistry and Molecular Biology, Saarland University, 66421 Homburg, Germany; (A.T.); (M.S.); (D.H.)
| | - Drazena Hadzibeganovic
- Department of Medical Biochemistry and Molecular Biology, Saarland University, 66421 Homburg, Germany; (A.T.); (M.S.); (D.H.)
| | - Sarah Haßdenteufel
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Sven Lang
- Department of Medical Biochemistry and Molecular Biology, Saarland University, 66421 Homburg, Germany; (A.T.); (M.S.); (D.H.)
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2
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Signal Peptide Peptidase-Type Proteases: Versatile Regulators with Functions Ranging from Limited Proteolysis to Protein Degradation. J Mol Biol 2020; 432:5063-5078. [DOI: 10.1016/j.jmb.2020.05.014] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2020] [Revised: 05/02/2020] [Accepted: 05/19/2020] [Indexed: 12/15/2022]
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The Metastable XBP1u Transmembrane Domain Defines Determinants for Intramembrane Proteolysis by Signal Peptide Peptidase. Cell Rep 2020; 26:3087-3099.e11. [PMID: 30865896 DOI: 10.1016/j.celrep.2019.02.057] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2018] [Revised: 12/07/2018] [Accepted: 02/14/2019] [Indexed: 11/23/2022] Open
Abstract
Unspliced XBP1 mRNA encodes XBP1u, the transcriptionally inert variant of the unfolded protein response (UPR) transcription factor XBP1s. XBP1u targets its mRNA-ribosome-nascent-chain-complex to the endoplasmic reticulum (ER) to facilitate UPR activation and prevents overactivation. Yet, its membrane association is controversial. Here, we use cell-free translocation and cellular assays to define a moderately hydrophobic stretch in XBP1u that is sufficient to mediate insertion into the ER membrane. Mutagenesis of this transmembrane (TM) region reveals residues that facilitate XBP1u turnover by an ER-associated degradation route that is dependent on signal peptide peptidase (SPP). Furthermore, the impact of these mutations on TM helix dynamics was assessed by residue-specific amide exchange kinetics, evaluated by a semi-automated algorithm. Based on our results, we suggest that SPP-catalyzed intramembrane proteolysis of TM helices is not only determined by their conformational flexibility, but also by side-chain interactions near the scissile peptide bond with the enzyme's active site.
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4
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Pinter N, Hach CA, Hampel M, Rekhter D, Zienkiewicz K, Feussner I, Poehlein A, Daniel R, Finkernagel F, Heimel K. Signal peptide peptidase activity connects the unfolded protein response to plant defense suppression by Ustilago maydis. PLoS Pathog 2019; 15:e1007734. [PMID: 30998787 PMCID: PMC6490947 DOI: 10.1371/journal.ppat.1007734] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2018] [Revised: 04/30/2019] [Accepted: 03/27/2019] [Indexed: 11/18/2022] Open
Abstract
The corn smut fungus Ustilago maydis requires the unfolded protein response (UPR) to maintain homeostasis of the endoplasmic reticulum (ER) during the biotrophic interaction with its host plant Zea mays (maize). Crosstalk between the UPR and pathways controlling pathogenic development is mediated by protein-protein interactions between the UPR regulator Cib1 and the developmental regulator Clp1. Cib1/Clp1 complex formation results in mutual modification of the connected regulatory networks thereby aligning fungal proliferation in planta, efficient effector secretion with increased ER stress tolerance and long-term UPR activation in planta. Here we address UPR-dependent gene expression and its modulation by Clp1 using combinatorial RNAseq/ChIPseq analyses. We show that increased ER stress resistance is connected to Clp1-dependent alterations of Cib1 phosphorylation, protein stability and UPR gene expression. Importantly, we identify by deletion screening of UPR core genes the signal peptide peptidase Spp1 as a novel key factor that is required for establishing a compatible biotrophic interaction between U. maydis and its host plant maize. Spp1 is dispensable for ER stress resistance and vegetative growth but requires catalytic activity to interfere with the plant defense, revealing a novel virulence specific function for signal peptide peptidases in a biotrophic fungal/plant interaction. Biotrophic pathogens establish compatible interactions with their host to cause disease. A critical step in this process is the suppression of plant defense responses by secreted effector proteins. In the maize infecting fungus Ustilago maydis expression of effector encoding genes is coordinately upregulated at defined stages of pathogenic development in so-called effector waves. Efficient secretion of the multitude of effectors relies on the unfolded protein response (UPR) to maintain homeostasis of the endoplasmic reticulum. Activation of the UPR is connected to the control of fungal proliferation through direct protein-protein interactions between the UPR regulator Cib1 and the developmental regulator Clp1. Here, we show that this interaction leads to functional modification of Cib1 and modulation of UPR gene expression to adapt the UPR for long-term activity in the plant. Within a core set of UPR regulated genes we identify the signal peptide peptidase Spp1 as a key factor for fungal virulence. We show that Spp1 requires its conserved catalytic activity to suppress the plant defense and cause disease. The virulence specific function of Spp1 does not involve pathways previously known to be associated with Spp1-like proteins or plant defense suppression, suggesting a novel role for Spp1 substrates in biotrophic interactions.
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Affiliation(s)
- Niko Pinter
- Department of Molecular Microbiology and Genetics, Institute of Microbiology and Genetics, Göttingen Center for Molecular Biosciences (GZMB), University of Göttingen, Göttingen, Germany
| | - Christina Andrea Hach
- Department of Molecular Microbiology and Genetics, Institute of Microbiology and Genetics, Göttingen Center for Molecular Biosciences (GZMB), University of Göttingen, Göttingen, Germany
| | - Martin Hampel
- Department of Molecular Microbiology and Genetics, Institute of Microbiology and Genetics, Göttingen Center for Molecular Biosciences (GZMB), University of Göttingen, Göttingen, Germany
| | - Dmitrij Rekhter
- Department of Plant Biochemistry, Albrecht-von-Haller-Institute for Plant Sciences, Göttingen Center for Molecular Biosciences (GZMB), University of Göttingen, Göttingen, Germany
| | - Krzysztof Zienkiewicz
- Department of Plant Biochemistry, Albrecht-von-Haller-Institute for Plant Sciences, Göttingen Center for Molecular Biosciences (GZMB), University of Göttingen, Göttingen, Germany
- Service Unit for Metabolomics and Lipidomics, Göttingen Center for Molecular Biosciences (GZMB), University of Göttingen, Göttingen, Germany
| | - Ivo Feussner
- Department of Plant Biochemistry, Albrecht-von-Haller-Institute for Plant Sciences, Göttingen Center for Molecular Biosciences (GZMB), University of Göttingen, Göttingen, Germany
- Service Unit for Metabolomics and Lipidomics, Göttingen Center for Molecular Biosciences (GZMB), University of Göttingen, Göttingen, Germany
| | - Anja Poehlein
- Department of Genomic and Applied Microbiology & Göttingen Genomics Laboratory, Institute of Microbiology and Genetics, University of Göttingen, Göttingen, Germany
| | - Rolf Daniel
- Department of Genomic and Applied Microbiology & Göttingen Genomics Laboratory, Institute of Microbiology and Genetics, University of Göttingen, Göttingen, Germany
| | - Florian Finkernagel
- Center for Tumor Biology and Immunology (ZTI), Institute of Molecular Biology and Tumor Research (IMT), Marburg, Germany
| | - Kai Heimel
- Department of Molecular Microbiology and Genetics, Institute of Microbiology and Genetics, Göttingen Center for Molecular Biosciences (GZMB), University of Göttingen, Göttingen, Germany
- * E-mail:
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5
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Kronenberg-Versteeg D, Eichmann M, Russell MA, de Ru A, Hehn B, Yusuf N, van Veelen PA, Richardson SJ, Morgan NG, Lemberg MK, Peakman M. Molecular Pathways for Immune Recognition of Preproinsulin Signal Peptide in Type 1 Diabetes. Diabetes 2018; 67:687-696. [PMID: 29343547 DOI: 10.2337/db17-0021] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/05/2017] [Accepted: 01/10/2018] [Indexed: 11/13/2022]
Abstract
The signal peptide region of preproinsulin (PPI) contains epitopes targeted by HLA-A-restricted (HLA-A0201, A2402) cytotoxic T cells as part of the pathogenesis of β-cell destruction in type 1 diabetes. We extended the discovery of the PPI epitope to disease-associated HLA-B*1801 and HLA-B*3906 (risk) and HLA-A*1101 and HLA-B*3801 (protective) alleles, revealing that four of six alleles present epitopes derived from the signal peptide region. During cotranslational translocation of PPI, its signal peptide is cleaved and retained within the endoplasmic reticulum (ER) membrane, implying it is processed for immune recognition outside of the canonical proteasome-directed pathway. Using in vitro translocation assays with specific inhibitors and gene knockout in PPI-expressing target cells, we show that PPI signal peptide antigen processing requires signal peptide peptidase (SPP). The intramembrane protease SPP generates cytoplasm-proximal epitopes, which are transporter associated with antigen processing (TAP), ER-luminal epitopes, which are TAP independent, each presented by different HLA class I molecules and N-terminal trimmed by ER aminopeptidase 1 for optimal presentation. In vivo, TAP expression is significantly upregulated and correlated with HLA class I hyperexpression in insulin-containing islets of patients with type 1 diabetes. Thus, PPI signal peptide epitopes are processed by SPP and loaded for HLA-guided immune recognition via pathways that are enhanced during disease pathogenesis.
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Affiliation(s)
- Deborah Kronenberg-Versteeg
- Department of Immunobiology, Faculty of Life Sciences and Medicine, King's College London, London, U.K.
- National Institute for Health Research, Biomedical Research Centre at Guy's and St. Thomas' Hospital Foundation Trust and King's College London, London, U.K
| | - Martin Eichmann
- Department of Immunobiology, Faculty of Life Sciences and Medicine, King's College London, London, U.K
| | - Mark A Russell
- Institute of Biomedical and Clinical Science, University of Exeter Medical School, Exeter, U.K
| | - Arnoud de Ru
- Department of Immunohematology and Blood Transfusion, Leiden University Medical Center, Leiden, the Netherlands
| | - Beate Hehn
- Center for Molecular Biology of Heidelberg University (ZMBH), DKFZ-ZMBH Alliance, Heidelberg, Germany
| | - Norkhairin Yusuf
- Department of Immunobiology, Faculty of Life Sciences and Medicine, King's College London, London, U.K
| | - Peter A van Veelen
- Department of Immunohematology and Blood Transfusion, Leiden University Medical Center, Leiden, the Netherlands
| | - Sarah J Richardson
- Institute of Biomedical and Clinical Science, University of Exeter Medical School, Exeter, U.K
| | - Noel G Morgan
- Institute of Biomedical and Clinical Science, University of Exeter Medical School, Exeter, U.K
| | - Marius K Lemberg
- Center for Molecular Biology of Heidelberg University (ZMBH), DKFZ-ZMBH Alliance, Heidelberg, Germany
| | - Mark Peakman
- Department of Immunobiology, Faculty of Life Sciences and Medicine, King's College London, London, U.K
- National Institute for Health Research, Biomedical Research Centre at Guy's and St. Thomas' Hospital Foundation Trust and King's College London, London, U.K
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6
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Schaefer B, Moriishi K, Behrends S. Insights into the mechanism of isoenzyme-specific signal peptide peptidase-mediated translocation of heme oxygenase. PLoS One 2017; 12:e0188344. [PMID: 29155886 PMCID: PMC5695791 DOI: 10.1371/journal.pone.0188344] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2017] [Accepted: 11/06/2017] [Indexed: 11/19/2022] Open
Abstract
It has recently been shown that signal peptide peptidase (SPP) can catalyze the intramembrane cleavage of heme oxygenase-1 (HO-1) that leads to translocation of HO-1 into the cytosol and nucleus. While there is consensus that translocated HO-1 promotes tumor progression and drug resistance, the physiological signals leading to SPP-mediated intramembrane cleavage of HO-1 and the specificity of the process remain unclear. In this study, we used co-immunoprecipitation and confocal laser scanning microscopy to investigate the translocation mechanism of HO-1 and its regulation by SPP. We show that HO-1 and the closely related HO-2 isoenzyme bind to SPP under normoxic conditions. Under hypoxic conditions SPP mediates intramembrane cleavage of HO-1, but not HO-2. In experiments with an inactive HO-1 mutant (H25A) we show that translocation is independent of the catalytic activity of HO-1. Studies with HO-1 / HO-2 chimeras indicate that the membrane anchor, the PEST-domain and the nuclear shuttle sequence of HO-1 are necessary for full cleavage and subsequent translocation under hypoxic conditions. In the presence of co-expressed exogenous SPP, the anchor and the PEST-domain are sufficient for translocation. Taken together, we identified the domains involved in HO-1 translocation and showed that SPP-mediated cleavage is isoform-specific and independent of HO-activity. A closer understanding of the translocation mechanism of HO-1 is of particular importance because nuclear HO-1 seems to lead to tumor progression and drug resistance.
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Affiliation(s)
- Bianca Schaefer
- Department of Pharmacology, Toxicology and Clinical Pharmacy, University of Braunschweig—Institute of Technology, Braunschweig, Germany
| | - Kohji Moriishi
- Department of Microbiology, Faculty of Medicine Yamanashi University, Yamanashi, Japan
| | - Soenke Behrends
- Department of Pharmacology, Toxicology and Clinical Pharmacy, University of Braunschweig—Institute of Technology, Braunschweig, Germany
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7
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Oliveira CC, van Hall T. Alternative Antigen Processing for MHC Class I: Multiple Roads Lead to Rome. Front Immunol 2015; 6:298. [PMID: 26097483 PMCID: PMC4457021 DOI: 10.3389/fimmu.2015.00298] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2015] [Accepted: 05/22/2015] [Indexed: 12/31/2022] Open
Abstract
The well described conventional antigen-processing pathway is accountable for most peptides that end up in MHC class I molecules at the cell surface. These peptides experienced liberation by the proteasome and transport by the peptide transporter TAP. However, there are multiple roads that lead to Rome, illustrated by the increasing number of alternative processing pathways that have been reported during last years. Interestingly, TAP-deficient individuals do not succumb to viral infections, suggesting that CD8 T cell immunity is sufficiently supported by alternative TAP-independent processing pathways. To date, a diversity of viral and endogenous TAP-independent peptides have been identified in the grooves of different MHC class I alleles. Some of these peptides are not displayed by normal TAP-positive cells and we therefore called them TEIPP, for “T-cell epitopes associated with impaired peptide processing.” TEIPPs are hidden self-antigens, are derived from normal housekeeping proteins, and are processed via unconventional processing pathways. Per definition, TEIPPs are presented via TAP-independent pathways, but recent data suggest that part of this repertoire still depend on proteasome and metalloprotease activity. An exception is the C-terminal peptide of the endoplasmic reticulum (ER)-membrane-spanning ceramide synthase Trh4 that is surprisingly liberated by the signal peptide peptidase (SPP), the proteolytic enzyme involved in cleaving leader sequences. The intramembrane cleaving SPP is thereby an important contributor of TAP-independent peptides. Its family members, like the Alzheimer’s related presenilins, might contribute as well, according to our preliminary data. Finally, alternative peptide routing is an emerging field and includes processes like the unfolded protein response, the ER-associated degradation, and autophagy-associated vesicular pathways. These data convince us that there is a world to be discovered in the field of unconventional antigen processing.
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Affiliation(s)
- Cláudia C Oliveira
- Department of Clinical Oncology, Leiden University Medical Center , Leiden , Netherlands
| | - Thorbald van Hall
- Department of Clinical Oncology, Leiden University Medical Center , Leiden , Netherlands
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8
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Boname JM, Bloor S, Wandel MP, Nathan JA, Antrobus R, Dingwell KS, Thurston TL, Smith DL, Smith JC, Randow F, Lehner PJ. Cleavage by signal peptide peptidase is required for the degradation of selected tail-anchored proteins. ACTA ACUST UNITED AC 2014; 205:847-62. [PMID: 24958774 PMCID: PMC4068138 DOI: 10.1083/jcb.201312009] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Intramembrane proteolytic cleavage by signal peptide peptidase is required for the turnover of some ER-resident, tail-anchored membrane proteins. The regulated turnover of endoplasmic reticulum (ER)–resident membrane proteins requires their extraction from the membrane lipid bilayer and subsequent proteasome-mediated degradation. Cleavage within the transmembrane domain provides an attractive mechanism to facilitate protein dislocation but has never been shown for endogenous substrates. To determine whether intramembrane proteolysis, specifically cleavage by the intramembrane-cleaving aspartyl protease signal peptide peptidase (SPP), is involved in this pathway, we generated an SPP-specific somatic cell knockout. In a stable isotope labeling by amino acids in cell culture–based proteomics screen, we identified HO-1 (heme oxygenase-1), the rate-limiting enzyme in the degradation of heme to biliverdin, as a novel SPP substrate. Intramembrane cleavage by catalytically active SPP provided the primary proteolytic step required for the extraction and subsequent proteasome-dependent degradation of HO-1, an ER-resident tail-anchored protein. SPP-mediated proteolysis was not limited to HO-1 but was required for the dislocation and degradation of additional tail-anchored ER-resident proteins. Our study identifies tail-anchored proteins as novel SPP substrates and a specific requirement for SPP-mediated intramembrane cleavage in protein turnover.
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Affiliation(s)
- Jessica M Boname
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge CB2 0XY, England, UK Department of Medicine, University of Cambridge, Cambridge CB2 0QQ, England, UK
| | - Stuart Bloor
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge CB2 0XY, England, UK Department of Medicine, University of Cambridge, Cambridge CB2 0QQ, England, UK
| | - Michal P Wandel
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge CB2 0XY, England, UK Division of Protein and Nucleic Acid Chemistry, Medical Research Council Laboratory of Molecular Biology, Cambridge CB2 0QH, England, UK
| | - James A Nathan
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge CB2 0XY, England, UK Department of Medicine, University of Cambridge, Cambridge CB2 0QQ, England, UK
| | - Robin Antrobus
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge CB2 0XY, England, UK
| | - Kevin S Dingwell
- Medical Research Council National Institute for Medical Research, London NW7 1AA, England, UK
| | - Teresa L Thurston
- Division of Protein and Nucleic Acid Chemistry, Medical Research Council Laboratory of Molecular Biology, Cambridge CB2 0QH, England, UK
| | - Duncan L Smith
- Cancer Research UK Manchester Institute, University of Manchester, Manchester M20 4B, England, UK
| | - James C Smith
- Medical Research Council National Institute for Medical Research, London NW7 1AA, England, UK
| | - Felix Randow
- Department of Medicine, University of Cambridge, Cambridge CB2 0QQ, England, UK Division of Protein and Nucleic Acid Chemistry, Medical Research Council Laboratory of Molecular Biology, Cambridge CB2 0QH, England, UK
| | - Paul J Lehner
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge CB2 0XY, England, UK Department of Medicine, University of Cambridge, Cambridge CB2 0QQ, England, UK
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9
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Voss M, Schröder B, Fluhrer R. Mechanism, specificity, and physiology of signal peptide peptidase (SPP) and SPP-like proteases. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1828:2828-39. [PMID: 24099004 DOI: 10.1016/j.bbamem.2013.03.033] [Citation(s) in RCA: 102] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/27/2012] [Revised: 03/25/2013] [Accepted: 03/29/2013] [Indexed: 01/09/2023]
Abstract
Signal peptide peptidase (SPP) and the homologous SPP-like (SPPL) proteases SPPL2a, SPPL2b, SPPL2c and SPPL3 belong to the family of GxGD intramembrane proteases. SPP/SPPLs selectively cleave transmembrane domains in type II orientation and do not require additional co-factors for proteolytic activity. Orthologues of SPP and SPPLs have been identified in other vertebrates, plants, and eukaryotes. In line with their diverse subcellular localisations ranging from the ER (SPP, SPPL2c), the Golgi (SPPL3), the plasma membrane (SPPL2b) to lysosomes/late endosomes (SPPL2a), the different members of the SPP/SPPL family seem to exhibit distinct functions. Here, we review the substrates of these proteases identified to date as well as the current state of knowledge about the physiological implications of these proteolytic events as deduced from in vivo studies. Furthermore, the present knowledge on the structure of intramembrane proteases of the SPP/SPPL family, their cleavage mechanism and their substrate requirements are summarised. This article is part of a Special Issue entitled: Intramembrane Proteases.
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Affiliation(s)
- Matthias Voss
- Adolf Butenandt Institute for Biochemistry, Ludwig-Maximilians University Munich, Schillerstr. 44, 80336 Munich, Germany
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10
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Oliveira CC, Querido B, Sluijter M, de Groot AF, van der Zee R, Rabelink MJWE, Hoeben RC, Ossendorp F, van der Burg SH, van Hall T. New role of signal peptide peptidase to liberate C-terminal peptides for MHC class I presentation. THE JOURNAL OF IMMUNOLOGY 2013; 191:4020-8. [PMID: 24048903 DOI: 10.4049/jimmunol.1301496] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
The signal peptide peptidase (SPP) is an intramembrane cleaving aspartyl protease involved in release of leader peptide remnants from the endoplasmic reticulum membrane, hence its name. We now found a new activity of SPP that mediates liberation of C-terminal peptides. In our search for novel proteolytic enzymes involved in MHC class I (MHC-I) presentation, we found that SPP generates the C-terminal peptide-epitope of a ceramide synthase. The display of this immunogenic peptide-MHC-I complex at the cell surface was independent of conventional processing components like proteasome and peptide transporter TAP. Absence of TAP activity even increased the MHC-I presentation of this Ag. Mutagenesis studies revealed the crucial role of the C-terminal location of the epitope and "helix-breaking" residues in the transmembrane region just upstream of the peptide, indicating that SPP directly liberated the minimal 9-mer peptide. Moreover, silencing of SPP and its family member SPPL2a led to a general reduction of surface peptide-MHC-I complexes, underlining the involvement of these enzymes in Ag processing and presentation.
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Affiliation(s)
- Cláudia C Oliveira
- Department of Clinical Oncology, Leiden University Medical Center, 2333 ZA Leiden, The Netherlands
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Pester O, Barrett PJ, Hornburg D, Hornburg P, Pröbstle R, Widmaier S, Kutzner C, Dürrbaum M, Kapurniotu A, Sanders CR, Scharnagl C, Langosch D. The backbone dynamics of the amyloid precursor protein transmembrane helix provides a rationale for the sequential cleavage mechanism of γ-secretase. J Am Chem Soc 2013; 135:1317-29. [PMID: 23265086 PMCID: PMC3560327 DOI: 10.1021/ja3112093] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The etiology of Alzheimer's disease depends on the relative abundance of different amyloid-β (Aβ) peptide species. These peptides are produced by sequential proteolytic cleavage within the transmembrane helix of the 99 residue C-terminal fragment of the amyloid precursor protein (C99) by the intramembrane protease γ-secretase. Intramembrane proteolysis is thought to require local unfolding of the substrate helix, which has been proposed to be cleaved as a homodimer. Here, we investigated the backbone dynamics of the substrate helix. Amide exchange experiments of monomeric recombinant C99 and of synthetic transmembrane domain peptides reveal that the N-terminal Gly-rich homodimerization domain exchanges much faster than the C-terminal cleavage region. MD simulations corroborate the differential backbone dynamics, indicate a bending motion at a diglycine motif connecting dimerization and cleavage regions, and detect significantly different H-bond stabilities at the initial cleavage sites. Our results are consistent with the following hypotheses about cleavage of the substrate: First, the GlyGly hinge may precisely position the substrate within γ-secretase such that its catalytic center must start proteolysis at the known initial cleavage sites. Second, the ratio of cleavage products formed by subsequent sequential proteolysis could be influenced by differential extents of solvation and by the stabilities of H-bonds at alternate initial sites. Third, the flexibility of the Gly-rich domain may facilitate substrate movement within the enzyme during sequential proteolysis. Fourth, dimerization may affect substrate processing by decreasing the dynamics of the dimerization region and by increasing that of the C-terminal part of the cleavage region.
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Affiliation(s)
- Oxana Pester
- Lehrstuhl Chemie der Biopolymere, Technische Universität München, Weihenstephaner Berg 3, 85354 Freising, and Munich Center For Integrated Protein Science (CIPS), Germany
| | - Paul J. Barrett
- Department of Biochemistry and Center for Structural Biology, Vanderbilt University School of Medicine, Nashville, Tennessee USA 37232-8725
| | - Daniel Hornburg
- Lehrstuhl Chemie der Biopolymere, Technische Universität München, Weihenstephaner Berg 3, 85354 Freising, and Munich Center For Integrated Protein Science (CIPS), Germany
| | - Philipp Hornburg
- Lehrstuhl Chemie der Biopolymere, Technische Universität München, Weihenstephaner Berg 3, 85354 Freising, and Munich Center For Integrated Protein Science (CIPS), Germany
| | - Rasmus Pröbstle
- Lehrstuhl Chemie der Biopolymere, Technische Universität München, Weihenstephaner Berg 3, 85354 Freising, and Munich Center For Integrated Protein Science (CIPS), Germany
| | - Simon Widmaier
- Lehrstuhl Chemie der Biopolymere, Technische Universität München, Weihenstephaner Berg 3, 85354 Freising, and Munich Center For Integrated Protein Science (CIPS), Germany
| | - Christoph Kutzner
- Lehrstuhl Chemie der Biopolymere, Technische Universität München, Weihenstephaner Berg 3, 85354 Freising, and Munich Center For Integrated Protein Science (CIPS), Germany
| | - Milena Dürrbaum
- Lehrstuhl Chemie der Biopolymere, Technische Universität München, Weihenstephaner Berg 3, 85354 Freising, and Munich Center For Integrated Protein Science (CIPS), Germany
| | - Aphrodite Kapurniotu
- Fachgebiet Peptidbiochemie, Technische Universität München, Emil-Erlenmeyer-Forum 5, 85354 Freising, Germany
| | - Charles R. Sanders
- Department of Biochemistry and Center for Structural Biology, Vanderbilt University School of Medicine, Nashville, Tennessee USA 37232-8725
| | - Christina Scharnagl
- Fakultät für Physik E14, Technische Universität München, Maximus-von-Imhof-Forum 4, 85354 Freising, Germany
| | - Dieter Langosch
- Lehrstuhl Chemie der Biopolymere, Technische Universität München, Weihenstephaner Berg 3, 85354 Freising, and Munich Center For Integrated Protein Science (CIPS), Germany
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12
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Identification and characterization of five intramembrane metalloproteases in Anabaena variabilis. J Bacteriol 2012; 194:6105-15. [PMID: 22961855 DOI: 10.1128/jb.01366-12] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Regulated intramembrane proteolysis (RIP) involves cleavage of a transmembrane segment of a protein, releasing the active form of a membrane-anchored transcription factor (MTF) or a membrane-tethered signaling protein in response to an extracellular or intracellular signal. RIP is conserved from bacteria to humans and governs many important signaling pathways in both prokaryotes and eukaryotes. Proteases that carry out these cleavages are named intramembrane cleaving proteases (I-CLips). To date, little is known about I-CLips in cyanobacteria. In this study, five putative site-2 type I-Clips (Ava_1070, Ava_1730, Ava_1797, Ava_3438, and Ava_4785) were identified through a genome-wide survey in Anabaena variabilis. Biochemical analysis demonstrated that these five putative A. variabilis site-2 proteases (S2Ps(Av)) have authentic protease activities toward an artificial substrate pro-σ(K), a Bacillus subtilis MTF, in our reconstituted Escherichia coli system. The enzymatic activities of processing pro-σ(K) differ among these five S2Ps(Av). Substitution of glutamic acid (E) by glutamine (Q) in the conserved HEXXH zinc-coordinated motif caused the loss of protease activities in these five S2Ps(Av), suggesting that they belonged to the metalloprotease family. Further mapping of the cleaved peptides of pro-σ(K) by Ava_4785 and Ava_1797 revealed that Ava_4785 and Ava_1797 recognized the same cleavage site in pro-σ(K) as SpoIVFB, a cognate S2P of pro-σ(K) from B. subtilis. Taking these results together, we report here for the first time the identification of five metallo-intramembrane cleaving proteases in Anabaena variabilis. The experimental system described herein should be applicable to studies of other RIP events and amenable to developing in vitro assays for I-CLips.
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13
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Jeyaraju DV, Sood A, Laforce-Lavoie A, Pellegrini L. Rhomboid proteases in mitochondria and plastids: keeping organelles in shape. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2012; 1833:371-80. [PMID: 22634239 DOI: 10.1016/j.bbamcr.2012.05.019] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/25/2012] [Revised: 05/10/2012] [Accepted: 05/17/2012] [Indexed: 01/16/2023]
Abstract
Rhomboids constitute the most widespread and conserved family of intramembrane cleaving proteases. They are key regulators of critical cellular processes in bacteria and animals, and are poised to play an equally important role also in plants. Among eukaryotes, a distinct subfamily of rhomboids, prototyped by the mammalian mitochondrial protein Parl, ensures the maintenance of the structural and functional integrity of mitochondria and plastids. Here, we discuss the studies that in the past decade have unveiled the role, regulation, and structure of this unique group of rhomboid proteases. This article is part of a Special Issue entitled: Protein Import and Quality Control in Mitochondria and Plastids.
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Affiliation(s)
- Danny V Jeyaraju
- Institut universitaire en santé mentale de Québec, Université Laval, Québec, Canada
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14
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Graham SJL, Dziadek MA, Johnstone LS. A cytosolic STIM2 preprotein created by signal peptide inefficiency activates ORAI1 in a store-independent manner. J Biol Chem 2011; 286:16174-85. [PMID: 21383014 DOI: 10.1074/jbc.m110.206946] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Calcium (Ca(2+)) influx through the plasma membrane store-operated Ca(2+) channel ORAI1 is controlled by Ca(2+) sensors of the stromal interaction molecule (STIM) family. STIM1 responds to endoplasmic reticulum (ER) Ca(2+) store depletion by redistributing and activating ORAI1 from regions of the ER juxtaposed to the plasma membrane. Unlike STIM1, STIM2 can regulate ORAI1 in a store-dependent and store-independent manner, but the mechanism by which this is achieved is unknown. Here we find that STIM2 is translated from a highly conserved methionine residue and is directed to the ER by an incredibly long 101-amino acid signal peptide. We find that although the majority of the total STIM2 population resides on the ER membrane, a second population escapes ER targeting to accumulate as a full-length preprotein in the cytosol, signal peptide intact. Unlike STIM2, preSTIM2 localizes to the inner leaflet of the plasma membrane where it interacts with ORAI1 to regulate basal Ca(2+) concentration and Ca(2+)-dependent gene transcription in a store-independent manner. Furthermore, a third protein comprising a fragment of the STIM2 signal peptide is released from the ER membrane into the cytosol where it regulates gene transcription in a Ca(2+)-independent manner. This study establishes a new model for STIM2-mediated regulation of ORAI1 in which two distinct proteins, STIM2 and preSTIM2, control store-dependent and store-independent modes of ORAI1 activation.
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Affiliation(s)
- Sarah J L Graham
- School of Biological Sciences, University of Auckland, Auckland, New Zealand
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15
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Signal peptide peptidase (SPP) assembles with substrates and misfolded membrane proteins into distinct oligomeric complexes. Biochem J 2010; 427:523-34. [PMID: 20196774 PMCID: PMC2860808 DOI: 10.1042/bj20091005] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
SPP (signal peptide peptidase) is an aspartyl intramembrane cleaving protease, which processes a subset of signal peptides, and is linked to the quality control of ER (endoplasmic reticulum) membrane proteins. We analysed SPP interactions with signal peptides and other membrane proteins by co-immunoprecipitation assays. We found that SPP interacts specifically and tightly with a large range of newly synthesized membrane proteins, including signal peptides, preproteins and misfolded membrane proteins, but not with all co-expressed type II membrane proteins. Signal peptides are trapped by the catalytically inactive SPP mutant SPPD/A. Preproteins and misfolded membrane proteins interact with both SPP and the SPPD/A mutant, and are not substrates for SPP-mediated intramembrane proteolysis. Proteins interacting with SPP are found in distinct complexes of different sizes. A signal peptide is mainly trapped in a 200 kDa SPP complex, whereas a preprotein is predominantly found in a 600 kDa SPP complex. A misfolded membrane protein is detected in 200, 400 and 600 kDa SPP complexes. We conclude that SPP not only processes signal peptides, but also collects preproteins and misfolded membrane proteins that are destined for disposal.
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16
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Ectodomain shedding and generation of two carboxy-terminal fragments of human complement receptor 2/CD21. Mol Immunol 2009; 46:2630-9. [DOI: 10.1016/j.molimm.2009.04.036] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2009] [Revised: 04/21/2009] [Accepted: 04/29/2009] [Indexed: 11/22/2022]
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17
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Human signal peptide had advantage over mouse in secretory expression. Histochem Cell Biol 2009; 132:239-46. [PMID: 19404667 DOI: 10.1007/s00418-009-0602-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/09/2009] [Indexed: 10/20/2022]
Abstract
The signal peptide is a critical component in the secretory expression of protein in eukaryotic cells. It has been verified that the signal peptide of mouse nerve growth factor could mediate the secretory expression of beta-endorphin in cultured non-neuronal cells. Although there is a counterpart of nerve growth factor in human genome, no research about the signal sequence from human genome has been reported. The function of mediating secretory expression is affected by many factors. We assumed that the counterpart from human genome could function as the signal peptide from mouse nerve growth factor does and these two signal sequences had different efficiency in mediating secretory expression of beta-endorphin, but we could not figure out which one had a better function. To validate our hypothesis and give an answer to the question, we constructed two eukaryotic vectors, pcDNA3.1-hEP and pcDNA3.1-mEP, containing human and mouse signal sequences in fusion genes, respectively. RT-PCR showed that the constructed fusion genes were expressed in NIH3T3 cells. We also found that the detected beta-endorphin by the immunofluorescent technique was mainly in the cytoplasm of NIH3T3 cells. The concentration of beta-endorphin in the culture medium by RIA is 280.33 +/- 24.16 (pg/ml) and 191.04 +/- 7.96 (pg/ml) from pcDNA3.1-hEP and pcDNA3.1-mEP, respectively, and there was a significant statistical difference between them (P < 0.05). A difference existed between them and that from blank vector individually (P < 0.01). These findings suggest that our constructed fusion gene containing the signal sequence of human nerve growth factor can be secretorily expressed and the efficiency of the signal peptide from human nerve growth factor is higher than that of mouse signal peptide.
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18
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Seo PJ, Kim SG, Park CM. Membrane-bound transcription factors in plants. TRENDS IN PLANT SCIENCE 2008; 13:550-6. [PMID: 18722803 DOI: 10.1016/j.tplants.2008.06.008] [Citation(s) in RCA: 145] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/17/2008] [Revised: 06/19/2008] [Accepted: 06/20/2008] [Indexed: 05/03/2023]
Abstract
The ability to activate dormant transcription factors is an important molecular feature of the transcriptional regulatory networks that govern diverse cellular functions. An intriguing example is the controlled proteolytic activation of membrane-bound transcription factors (MTFs). Most MTFs are activated either by intramembrane proteases or by the ubiquitin-proteasome pathway. Recent studies have shown that several members of the bZIP and NAC families in Arabidopsis are membrane-associated and are activated by membrane-associated proteases during stress responses in the endoplasmic reticulum and when the plants experience environmental stresses. A genome-scale analysis shows that over 10% of all transcription factors are membrane bound, indicating that activation of MTFs occurs at the genomic level, allowing transcription to be regulated rapidly under stressful conditions.
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Affiliation(s)
- Pil Joon Seo
- Molecular Signaling Laboratory, Department of Chemistry, Seoul National University, Seoul 151-742, Korea
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19
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The C-terminal PAL motif and transmembrane domain 9 of presenilin 1 are involved in the formation of the catalytic pore of the gamma-secretase. J Neurosci 2008; 28:6264-71. [PMID: 18550769 DOI: 10.1523/jneurosci.1163-08.2008] [Citation(s) in RCA: 118] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Gamma-secretase is an unusual membrane-embedded protease, which cleaves the transmembrane domains (TMDs) of type I membrane proteins, including amyloid-beta precursor protein and Notch receptor. We have previously shown the existence of a hydrophilic pore formed by TMD6 and TMD7 of presenilin 1 (PS1), the catalytic subunit of gamma-secretase, within the membrane by the substituted cysteine accessibility method. Here we analyzed the structure of TMD8, TMD9, and the C terminus of PS1, which encompass the conserved PAL motif and the hydrophobic C-terminal tip, both being critical for the catalytic activity and the formation of the gamma-secretase complex. We found that the amino acid residues around the PAL motif and the extracellular/luminal portion of TMD9 are highly water accessible and located in proximity to the catalytic pore. Furthermore, the region starting from the luminal end of TMD9 toward the C terminus forms an amphipathic alpha-helix-like structure that extends along the interface between the membrane and the extracellular milieu. Competition analysis using gamma-secretase inhibitors revealed that the TMD9 is involved in the initial binding of substrates, as well as in the subsequent catalytic process as a subsite. Our results provide mechanistic insights into the role of TMD9 in the formation of the catalytic pore and the substrate entry, crucial to the unusual mode of intramembrane proteolysis by gamma-secretase.
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20
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Targett-Adams P, Hope G, Boulant S, McLauchlan J. Maturation of hepatitis C virus core protein by signal peptide peptidase is required for virus production. J Biol Chem 2008; 283:16850-9. [PMID: 18424431 DOI: 10.1074/jbc.m802273200] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Complete maturation of hepatitis C virus (HCV) core protein requires coordinate cleavage by signal peptidase and an intramembrane protease, signal peptide peptidase. We show that reducing the intracellular levels of signal peptide peptidase lowers the titer of infectious virus released from cells, indicating that it plays an important role in virus production. Proteolysis by the enzyme at a signal peptide between core and the E1 glycoprotein is needed to permit targeting of core to lipid droplets. From mutagenesis studies, introducing mutations into the core-E1 signal peptide delayed the appearance of signal peptide peptidase-processed core until between 48 and 72 h after the beginning of the infectious cycle. Accumulation of mature core at these times coincided with its localization to lipid droplets and a rise in titer of infectious HCV. Therefore, processing of core by signal peptide peptidase is a critical event in the virus life cycle. To study the stage in virus production that may be blocked by interfering with intramembrane cleavage of core, we examined the distribution of viral RNA in cells harboring the core-E1 signal peptide mutant. Results revealed that colocalization of core with HCV RNA required processing of the protein by signal peptide peptidase. Our findings provide new insights into the sequence requirements for proteolysis by signal peptide peptidase. Moreover, they offer compelling evidence for a function for an intramembrane protease to facilitate the association of core with viral genomes, thereby creating putative sites for assembly of nascent virus particles.
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Affiliation(s)
- Paul Targett-Adams
- MRC Virology Unit, Institute of Virology, Glasgow G11 5JR, United Kingdom
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21
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Abstract
Rhomboids were only discovered to be novel proteases in 2001, but progress on understanding this newest family of intramembrane proteases has been rapid. They are now the best characterized of these rather mysterious enzymes that cleave transmembrane domains within the lipid bilayer. In particular, the biochemical analysis of solubilized rhomboids and, most recently, a flurry of high-resolution crystal structures, have led to real insight into their enzymology. Long-standing questions about how it is possible for a water-requiring proteolytic reaction to occur in the lipid bilayer are now answered for the rhomboids. Intramembrane proteases, which control many medically important biological processes, have made the transition from rather heretical outsiders to novel enzymes that are becoming well understood.
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22
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Characterization of the sequence specificity determinants required for processing and control of sex pheromone by the intramembrane protease Eep and the plasmid-encoded protein PrgY. J Bacteriol 2007; 190:1172-83. [PMID: 18083822 DOI: 10.1128/jb.01327-07] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Conjugative transfer of the Enterococcus faecalis plasmid pCF10 is induced by the peptide pheromone cCF10 when recipient-produced cCF10 is detected by donors. cCF10 is produced by proteolytic processing of the signal sequence of a chromosomally encoded lipoprotein (CcfA). In donors, endogenously produced cCF10 is carefully controlled to prevent constitutive expression of conjugation functions, an energetically wasteful process, except in vivo, where endogenous cCF10 induces a conjugation-linked virulence factor. Endogenous cCF10 is controlled by two plasmid-encoded products; a membrane protein PrgY reduces pheromone levels in donors, and a secreted inhibitor peptide iCF10 inhibits the residual endogenous pheromone that escapes PrgY control. In this study we genetically determined the amino acid specificity determinants within PrgY, cCF10, and the cCF10 precursor that are necessary for cCF10 processing and for PrgY-mediated control. We showed that amino acid residues 125 to 241 of PrgY are required for specific recognition of cCF10 and that PrgY recognizes determinants within the heptapeptide cCF10 sequence, supporting a direct interaction between PrgY and mature cCF10. In addition, we found that a regulated intramembrane proteolysis (RIP) family pheromone precursor-processing protein Eep recognizes amino acids N-terminal to cCF10 in the signal sequence of CcfA. These results support a model where Eep directly targets pheromone precursors for RIP and PrgY interacts directly with the mature cCF10 peptide during processing. Despite evidence that both PrgY and Eep associate with cCF10 in or near the membrane, results presented here indicate that these two proteins function independently.
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23
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Ma HC, Ku YY, Hsieh YC, Lo SY. Characterization of the cleavage of signal peptide at the C-terminus of hepatitis C virus core protein by signal peptide peptidase. J Biomed Sci 2007; 14:31-41. [PMID: 17237979 PMCID: PMC7088784 DOI: 10.1007/s11373-006-9127-1] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2006] [Accepted: 10/08/2006] [Indexed: 12/22/2022] Open
Abstract
Production of hepatitis C virus (HCV) core protein requires the cleavages of polyprotein by signal peptidase and signal peptide peptidase (SPP). Cleavage of signal peptide at the C-terminus of HCV core protein by SPP was characterized in this study. The spko mutant (mutate a.a. 189-193 from ASAYQ to PPFPF) is more efficient than the A/F mutant (mutate a.a 189 and 191 from A to F) in blocking the cleavage of signal peptide by signal peptidase. The cleavage efficiency of SPP is inversely proportional to the length of C-terminal extension of the signal peptide: the longer the extension, the less efficiency the cleavage is. Thus, reducing the length of C-terminal extension of signal peptide by signal peptidase cleavage could facilitate further cleavage by SPP. The recombinant core protein fused with signal peptide from the C-terminus of p7 protein, but not those from the C-termini of E1 and E2, could be cleaved by SPP. Therefore, the sequence of the signal peptide is important but not the sole determinant for its cleavage by SPP. Replacement of the HCV core protein E.R.-associated domain (a.a. 120-150) with the E.R.-associated domain (a.a.1-50) of SARS-CoV membrane protein results in the failure of cleavage of this recombinant protein by SPP, though this protein still is E.R.-associated. This result suggests that not only E.R.-association but also specific protein sequence is important for the HCV core protein signal peptide cleavage by SPP. Thus, our results suggest that both sequences of the signal peptide and the E.R.-associated domain are important for the signal peptide cleavage of HCV core protein by SPP.
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Affiliation(s)
- Hsin-Chieh Ma
- Graduate Institute of Medical Sciences, Tzu Chi University, Hualien, Taiwan, ROC
| | - Yi-Yung Ku
- Graduate Institute of Molecular and Cellular Biology, Tzu Chi University, Hualien, Taiwan, ROC
| | - Yi-Ching Hsieh
- Graduate Institute of Molecular and Cellular Biology, Tzu Chi University, Hualien, Taiwan, ROC
| | - Shih-Yen Lo
- Graduate Institute of Medical Sciences, Tzu Chi University, Hualien, Taiwan, ROC
- Graduate Institute of Molecular and Cellular Biology, Tzu Chi University, Hualien, Taiwan, ROC
- Department of Laboratory Medicine and Biotechnology, Tzu Chi University, 701, Section 3, Chung Yang Road, Hualien, Taiwan, ROC
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24
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Nyborg AC, Herl L, Berezovska O, Thomas AV, Ladd TB, Jansen K, Hyman BT, Golde TE. Signal peptide peptidase (SPP) dimer formation as assessed by fluorescence lifetime imaging microscopy (FLIM) in intact cells. Mol Neurodegener 2006; 1:16. [PMID: 17105660 PMCID: PMC1654158 DOI: 10.1186/1750-1326-1-16] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2006] [Accepted: 11/14/2006] [Indexed: 11/13/2022] Open
Abstract
Background Signal peptide peptidase (SPP) is an intramembrane cleaving protease identified by its cleavage of several type II membrane signal peptides. Conservation of intramembrane active site residues demonstrates that SPP, SPP family members, and presenilins (PSs) make up a family of intramembrane cleaving proteases. Because SPP appears to function without additional protein cofactors, the study of SPP may provide structural insights into the mechanism of intramembrane proteolysis by this biomedically important family of proteins. Previous studies have shown that SPP isolated from cells appears to be a homodimer, but some evidence exists that in vitro SPP may be active as a monomer. We have conducted additional experiments to determine if SPP exists as a monomer or dimer in vivo. Results Fluorescence lifetime imaging microscopy (FLIM) can be is used to determine intra- or intermolecular interactions by fluorescently labeling epitopes on one or two different molecules. If the donor and acceptor fluorophores are less than 10 nm apart, the donor fluorophore lifetime shortens proportionally to the distance between the fluorophores. In this study, we used two types of fluorescence energy transfer (FRET) pairs; cyan fluorescent protein (CFP) with yellow fluorescent protein (YFP) or Alexa 488 with Cy3 to differentially label the NH2- or COOH-termini of SPP molecules. A cell based SPP activity assay was used to show that all tagged SPP proteins are proteolytically active. Using FLIM we were able to show that the donor fluorophore lifetime of the CFP tagged SPP construct in living cells significantly decreases when either a NH2- or COOH-terminally YFP tagged SPP construct is co-transfected, indicating close proximity between two different SPP molecules. These data were then confirmed in cell lines stably co-expressing V5- and FLAG-tagged SPP constructs. Conclusion Our FLIM data strongly suggest dimer formation between two separate SPP proteins. Although the tagged SPP constructs are expressed throughout the cell, SPP dimer detection by FLIM is seen predominantly at or near the plasma membrane.
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Affiliation(s)
- Andrew C Nyborg
- Department of Neuroscience, Mayo Clinic Jacksonville, Mayo Clinic College of Medicine, Jacksonville, Florida 32224, USA
| | - Lauren Herl
- Alzheimer's Disease Research Unit, Massachusetts Institute for Neurodegenerative Diseases, Massachusetts General Hospital, Charlestown, Massachusetts 02129, USA
| | - Oksana Berezovska
- Alzheimer's Disease Research Unit, Massachusetts Institute for Neurodegenerative Diseases, Massachusetts General Hospital, Charlestown, Massachusetts 02129, USA
| | - Anne V Thomas
- Alzheimer's Disease Research Unit, Massachusetts Institute for Neurodegenerative Diseases, Massachusetts General Hospital, Charlestown, Massachusetts 02129, USA
| | - Thomas B Ladd
- Department of Neuroscience, Mayo Clinic Jacksonville, Mayo Clinic College of Medicine, Jacksonville, Florida 32224, USA
| | - Karen Jansen
- Department of Neuroscience, Mayo Clinic Jacksonville, Mayo Clinic College of Medicine, Jacksonville, Florida 32224, USA
| | - Bradley T Hyman
- Alzheimer's Disease Research Unit, Massachusetts Institute for Neurodegenerative Diseases, Massachusetts General Hospital, Charlestown, Massachusetts 02129, USA
| | - Todd E Golde
- Department of Neuroscience, Mayo Clinic Jacksonville, Mayo Clinic College of Medicine, Jacksonville, Florida 32224, USA
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25
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Nyborg AC, Ladd TB, Jansen K, Kukar T, Golde TE. Intramembrane proteolytic cleavage by human signal peptide peptidase like 3 and malaria signal peptide peptidase. FASEB J 2006; 20:1671-9. [PMID: 16873890 DOI: 10.1096/fj.06-5762com] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Signal peptide peptidase (SPP) is an intramembrane cleaving protease (I-CLiP) identified by its cleavage of several type II membrane signal peptides. To date, only human SPP has been directly shown to have proteolytic activity. Here we demonstrate that the most closely related human homologue of SPP, signal peptide peptidase like 3 (SPPL3), cleaves a SPP substrate, but a more distantly related homologue, signal peptide peptidase like 2b (SPPL2b), does not. These data provide strong evidence that the SPP and SPPL3 have conserved active sites and suggest that the active sites SPPL2b is distinct. We have also synthesized a cDNA designed to express the single SPP gene present in Plasmodium falciparum and cloned this into a mammalian expression vector. When the malaria SPP protein is expressed in mammalian cells it cleaves a SPP substrate. Notably, several human SPP inhibitors block the proteolytic activity of malarial SPP (mSPP). Studies from several model organisms that express multiple SPP homologs demonstrate that the silencing of a single SPP homologue is lethal. Based on these data, we hypothesize that mSPP is a potential a novel therapeutic target for malaria.
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Affiliation(s)
- Andrew C Nyborg
- Department of Neuroscience, Mayo Clinic Jacksonville, Mayo Clinic College of Medicine, 4500 San Pablo Rd., Jacksonville, Florida 32224, USA
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26
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Targett-Adams P, Schaller T, Hope G, Lanford RE, Lemon SM, Martin A, McLauchlan J. Signal Peptide Peptidase Cleavage of GB Virus B Core Protein Is Required for Productive Infection in Vivo. J Biol Chem 2006; 281:29221-7. [PMID: 16882659 DOI: 10.1074/jbc.m605373200] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Chronic infection by hepatitis C virus (HCV) is a leading cause of liver disease for which better therapies are urgently needed. Because a clearer understanding of the viral life cycle may suggest novel anti-viral approaches, we studied the role of host signal peptide peptidase (SPP) in viral infection. This intramembrane protease cleaves within a C-terminal signal sequence in the viral core protein, but the molecular determinants of cleavage and whether it is required for infection in vivo are unknown. To answer these questions, we studied SPP processing in GB virus B (GBV-B) infection. GBV-B is the closest phylogenetic relative of HCV and offers an accurate surrogate model for HCV infection. We demonstrate that SPP also processes GBV-B core protein and that a serine residue in the hydrophobic region of the signal sequence (present also in HCV) is critical for efficient SPP cleavage. The small size of the serine side chain combined with its ability to form intra- and interhelical hydrogen bonds likely contributes to recognition of the signal sequence as a substrate for SPP. By introducing mutations with differing effects on SPP processing into an infectious GBV-B molecular clone, we demonstrate that SPP processing of the core protein is required for productive infection in primates. These results broaden our understanding of the mechanism and requirements for SPP cleavage and reveal a functional role in vivo for intramembrane proteolysis in host-pathogen interactions. Moreover, they identify SPP as a potential therapeutic target for reducing the impact of HCV infection.
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Affiliation(s)
- Paul Targett-Adams
- Medical Research Council Virology Unit, Church Street, Glasgow, G11 5JR, United Kingdom
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27
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Campo N, Rudner DZ. A branched pathway governing the activation of a developmental transcription factor by regulated intramembrane proteolysis. Mol Cell 2006; 23:25-35. [PMID: 16818230 DOI: 10.1016/j.molcel.2006.05.019] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2006] [Revised: 03/20/2006] [Accepted: 05/02/2006] [Indexed: 11/22/2022]
Abstract
The proteolytic activation of the membrane-associated transcription factor pro-sigma(K) is controlled by a signal transduction pathway during sporulation in the bacterium Bacillus subtilis. The pro-sigma(K) processing enzyme SpoIVFB, a membrane-embedded metalloprotease, is held inactive by two other integral-membrane proteins, SpoIVFA and BofA. We demonstrate that the signaling protease SpoIVB (IVB) triggers pro-sigma(K) processing by cleaving the extracellular domain of the SpoIVFA regulator at multiple sites. In vitro, these cleavages do not disrupt the interactions between SpoIVFA, SpoIVFB, and BofA, suggesting that IVB-dependent activation of the processing enzyme results from a conformational change in this complex. Our data further suggest that when IVB is unable to cleave SpoIVFA, it can still activate pro-sigma(K) processing through a second protease, CtpB. Finally, we demonstrate that CtpB, like IVB, triggers pro-sigma(K) processing by cleaving SpoIVFA. We propose that IVB regulates intramembrane proteolysis through two proteolytic pathways, both of which converge on the same regulator.
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Affiliation(s)
- Nathalie Campo
- Department of Microbiology and Molecular Genetics, Harvard Medical School, 200 Longwood Avenue, Boston, Massachusetts 02115, USA
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28
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Loureiro J, Lilley BN, Spooner E, Noriega V, Tortorella D, Ploegh HL. Signal peptide peptidase is required for dislocation from the endoplasmic reticulum. Nature 2006; 441:894-7. [PMID: 16738546 DOI: 10.1038/nature04830] [Citation(s) in RCA: 112] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2006] [Accepted: 04/18/2006] [Indexed: 11/08/2022]
Abstract
Human cytomegalovirus (HCMV) prevents the display of class I major histocompatibility complex (MHC) peptide complexes at the surface of infected cells as a means of escaping immune detection. Two HCMV-encoded immunoevasins, US2 and US11, induce the dislocation of class I MHC heavy chains from the endoplasmic reticulum membrane and target them for proteasomal degradation in the cytosol. Although the outcome of the dislocation reactions catalysed is similar, US2 and US11 operate differently: Derlin-1 is a key component of the US11 but not the US2 pathway. So far, proteins essential for US2-dependent dislocation have not been identified. Here we compare interacting partners of wild-type US2 with those of a dislocation-incompetent US2 mutant, and identify signal peptide peptidase (SPP) as a partner for the active form of US2. We show that a decrease in SPP levels by RNA-mediated interference inhibits heavy-chain dislocation by US2 but not by US11. Our data implicate SPP in the US2 pathway and indicate the possibility of a previously unknown function for this intramembrane-cleaving aspartic protease in dislocation from the endoplasmic reticulum.
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Affiliation(s)
- Joana Loureiro
- Department of Pathology, Harvard Medical School, Boston, Massachusetts 02115, USA
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Abstract
Relatively small genomes and high replication rates allow viruses and bacteria to accumulate mutations. This continuously presents the host immune system with new challenges. On the other side of the trenches, an increasingly well-adjusted host immune response, shaped by coevolutionary history, makes a pathogen's life a rather complicated endeavor. It is, therefore, no surprise that pathogens either escape detection or modulate the host immune response, often by redirecting normal cellular pathways to their advantage. For the purpose of this chapter, we focus mainly on the manipulation of the class I and class II major histocompatibility complex (MHC) antigen presentation pathways and the ubiquitin (Ub)-proteasome system by both viral and bacterial pathogens. First, we describe the general features of antigen presentation pathways and the Ub-proteasome system and then address how they are manipulated by pathogens. We discuss the many human cytomegalovirus (HCMV)-encoded immunomodulatory genes that interfere with antigen presentation (immunoevasins) and focus on the HCMV immunoevasins US2 and US11, which induce the degradation of class I MHC heavy chains by the proteasome by catalyzing their export from the endoplasmic reticulum (ER)-membrane into the cytosol, a process termed ER dislocation. US2- and US11-mediated subversion of ER dislocation ensures proteasomal degradation of class I MHC molecules and presumably allows HCMV to avoid recognition by cytotoxic T cells, whilst providing insight into general aspects of ER-associated degradation (ERAD) which is used by eukaryotic cells to purge their ER of defective proteins. We discuss the similarities and differences between the distinct pathways co-opted by US2 and US11 for dislocation and degradation of human class I MHC molecules and also a putatively distinct pathway utilized by the murine herpes virus (MHV)-68 mK3 immunoevasin for ER dislocation of murine class I MHC. We speculate on the implications of the three pathogen-exploited dislocation pathways to cellular ER quality control. Moreover, we discuss the ubiquitin (Ub)-proteasome system and its position at the core of antigen presentation as proteolysis and intracellular trafficking rely heavily on Ub-dependent processes. We add a few examples of manipulation of the Ub-proteasome system by pathogens in the context of the immune system and such diverse aspects of the host-pathogen relationship as virus budding, bacterial chromosome integration, and programmed cell death, to name a few. Finally, we speculate on newly found pathogen-encoded deubiquitinating enzymes (DUBs) and their putative roles in modulation of host-pathogen interactions.
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Affiliation(s)
- Joana Loureiro
- Whitehead Institute, 9 Cambridge Center, Cambridge, Massachusetts, USA
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Matsumi R, Atomi H, Imanaka T. Biochemical properties of a putative signal peptide peptidase from the hyperthermophilic archaeon Thermococcus kodakaraensis KOD1. J Bacteriol 2005; 187:7072-80. [PMID: 16199578 PMCID: PMC1251612 DOI: 10.1128/jb.187.20.7072-7080.2005] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
We have performed the first biochemical characterization of a putative archaeal signal peptide peptidase (SppA(Tk)) from the hyperthermophilic archaeon Thermococcus kodakaraensis KOD1. SppA(Tk), comprised of 334 residues, was much smaller than its counterpart from Escherichia coli (618 residues) and harbored a single predicted transmembrane domain near its N terminus. A truncated mutant protein without the N-terminal 54 amino acid residues (deltaN54SppA(Tk)) was found to be stable against autoproteolysis and was examined further. DeltaN54SppA(Tk) exhibited peptidase activity towards fluorogenic peptide substrates and was found to be highly thermostable. Moreover, the enzyme displayed a remarkable stability and preference for alkaline pH, with optimal activity detected at pH 10. DeltaN54SppA(Tk) displayed a K(m) of 240 +/- 18 microM and a V(max) of 27.8 +/- 0.7 micromol min(-1) mg(-1) towards Ala-Ala-Phe-4-methyl-coumaryl-7-amide at 80 degrees C and pH 10. The substrate specificity of the enzyme was examined in detail with a FRETS peptide library. By analyzing the cleavage products with liquid chromatography-mass spectrometry, deltaN54SppA(Tk) was found to efficiently cleave peptides with a relatively small side chain at the P-1 position and a hydrophobic or aromatic residue at the P-3 position. The positively charged Arg residue was preferred at the P-4 position, while substrates with negatively charged residues at the P-2, P-3, or P-4 position were not cleaved. When predicted signal sequences from the T. kodakaraensis genome sequence were examined, we found that the substrate specificity of deltaN54SppA(Tk) was in good agreement with its presumed role as a signal peptide peptidase in this archaeon.
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Affiliation(s)
- Rie Matsumi
- Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan
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31
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Becker-Herman S, Arie G, Medvedovsky H, Kerem A, Shachar I. CD74 is a member of the regulated intramembrane proteolysis-processed protein family. Mol Biol Cell 2005; 16:5061-9. [PMID: 16107560 PMCID: PMC1266406 DOI: 10.1091/mbc.e05-04-0327] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Quite a few regulatory proteins, including transcription factors, are normally maintained in a dormant state to be activated after internal or environmental cues. Recently, a novel strategy, requiring proteolytic cleavage, was described for the mobilization of dormant transcription factors. These transcription factors are initially synthesized in an inactive form, whereas "nesting" in integral membrane precursor proteins. After a cleavage event, these new active factors are released from the membrane and can migrate into the nucleus to drive regulated gene transcription. This mechanism, regulated intramembrane proteolysis (RIP), controls diverse biological processes in prokaryotes and eukaryotes in response to a variety of signals. The MHC class II chaperone, CD74 (invariant chain, Ii), was previously shown to function as a signaling molecule in several pathways. Recently, we demonstrated that after intramembranal cleavage, the CD74 cytosolic fragment (CD74-ICD) is released and induces activation of transcription mediated by the NF-kappaB p65/RelA homodimer and the B-cell-enriched coactivator, TAF(II)105. Here, we add CD74 to the growing family of RIP-processed proteins. Our studies show that CD74 ectodomain must be processed in the endocytic compartments to allow its intramembrane cleavage that liberates CD74 intracellular domain (CD74-ICD). We demonstrate that CD74-ICD translocates to the nucleus and induces the activation of the p65 member of NF-kappaB in this compartment.
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Higy M, Junne T, Spiess M. Topogenesis of membrane proteins at the endoplasmic reticulum. Biochemistry 2004; 43:12716-22. [PMID: 15461443 DOI: 10.1021/bi048368m] [Citation(s) in RCA: 119] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Most eukaryotic membrane proteins are cotranslationally integrated into the endoplasmic reticulum membrane by the Sec61 translocation complex. They are targeted to the translocon by hydrophobic signal sequences, which induce the translocation of either their N- or their C-terminal sequence. Signal sequence orientation is largely determined by charged residues flanking the apolar sequence (the positive-inside rule), folding properties of the N-terminal segment, and the hydrophobicity of the signal. Recent in vivo experiments suggest that N-terminal signals initially insert into the translocon head-on to yield a translocated N-terminus. Driven by a local electrical potential, the signal may invert its orientation and translocate the C-terminal sequence. Increased hydrophobicity slows down inversion by stabilizing the initial bound state. In vitro cross-linking studies indicate that signals rapidly contact lipids upon entering the translocon. Together with the recent crystal structure of the homologous SecYEbeta translocation complex of Methanococcus jannaschii, which did not reveal an obvious hydrophobic binding site for signals within the pore, a model emerges in which the translocon allows the lateral partitioning of hydrophobic segments between the aqueous pore and the lipid membrane. Signals may return into the pore for reorientation until translation is terminated. Subsequent transmembrane segments in multispanning proteins behave similarly and contribute to the overall topology of the protein.
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Affiliation(s)
- Marie Higy
- Biozentrum, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland
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Akiyama Y, Kanehara K, Ito K. RseP (YaeL), an Escherichia coli RIP protease, cleaves transmembrane sequences. EMBO J 2004; 23:4434-42. [PMID: 15496982 PMCID: PMC526465 DOI: 10.1038/sj.emboj.7600449] [Citation(s) in RCA: 142] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2004] [Accepted: 09/23/2004] [Indexed: 11/09/2022] Open
Abstract
Escherichia coli RseP (formerly YaeL) is believed to function as a 'regulated intramembrane proteolysis' (RIP) protease that introduces the second cleavage into anti-sigma(E) protein RseA at a position within or close to the transmembrane segment. However, neither its enzymatic activity nor the substrate cleavage position has been established. Here, we show that RseP-dependent cleavage indeed occurs within predicted transmembrane sequences of membrane proteins in vivo. Moreover, RseP catalyzed the same specificity proteolysis in an in vitro reaction system using purified components. Our in vivo and in vitro results show that RseP can cleave transmembrane sequences of some model membrane proteins that are unrelated to RseA, provided that the transmembrane region contains residues of low helical propensity. These results show that RseP has potential ability to cut a broad range of membrane protein sequences. Intriguingly, it is nevertheless recruited to the sigma(E) stress-response cascade as a specific player of RIP.
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Affiliation(s)
- Yoshinori Akiyama
- Institute for Virus Research, Kyoto University, Kyoto, Japan
- Institute for Virus Research, Kyoto University, Kyoto 606-8507, Japan. Tel.: +81 75 751 4040; Fax: +81 75 761 5626 or +81 75 771 5699; E-mail:
| | - Kazue Kanehara
- Institute for Virus Research, Kyoto University, Kyoto, Japan
| | - Koreaki Ito
- Institute for Virus Research, Kyoto University, Kyoto, Japan
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Friedmann E, Lemberg MK, Weihofen A, Dev KK, Dengler U, Rovelli G, Martoglio B. Consensus analysis of signal peptide peptidase and homologous human aspartic proteases reveals opposite topology of catalytic domains compared with presenilins. J Biol Chem 2004; 279:50790-8. [PMID: 15385547 DOI: 10.1074/jbc.m407898200] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The human genome encodes seven intramembrane-cleaving GXGD aspartic proteases. These are the two presenilins that activate signaling molecules and are implicated in Alzheimer's disease, signal peptide peptidase (SPP), required for immune surveillance, and four SPP-like candidate proteases (SPPLs), of unknown function. Here we describe a comparative analysis of the topologies of SPP and its human homologues, SPPL2a, -2b, -2c, and -3. We demonstrate that their N-terminal extensions are located in the extracellular space and, except for SPPL3, are modified with N-glycans. Whereas SPPL2a, -2b, and -2c contain a signal sequence, SPP and SPPL3 contain a type I signal anchor sequence for initiation of protein translocation and membrane insertion. The hydrophilic loops joining the transmembrane regions, which contain the catalytic residues, are facing the exoplasm. The C termini of all these proteins are exposed toward the cytosol. Taken together, our study demonstrates that SPP and its homologues are all of the same principal structure with a catalytic domain embedded in the membrane in opposite orientation to that of presenilins. Other than presenilins, SPPL2a, -2b, -2c, and -3 are therefore predicted to cleave type II-oriented substrate peptides like the prototypic protease SPP.
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Affiliation(s)
- Elena Friedmann
- Institute of Biochemistry, Swiss Federal Institute of Technology (ETH), ETH-Hoenggerberg, 8093 Zurich, Switzerland
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35
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Nyborg AC, Jansen K, Ladd TB, Fauq A, Golde TE. A signal peptide peptidase (SPP) reporter activity assay based on the cleavage of type II membrane protein substrates provides further evidence for an inverted orientation of the SPP active site relative to presenilin. J Biol Chem 2004; 279:43148-56. [PMID: 15252014 DOI: 10.1074/jbc.m405879200] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Signal peptide peptidase (SPP) is an intramembrane-cleaving protease identified by its cleavage of several type II membrane signal peptides after signal peptidase cleavage. Here we describe a novel, quantitative, cell-based SPP reporter assay. This assay utilizes a substrate consisting of the NH2 terminus of the ATF6 transcription factor fused to a transmembrane domain susceptible to SPP cleavage in vitro. In cells, cleavage of the substrate releases ATF6 from the membrane. This cleavage can be monitored by detection of an epitope that is unmasked in the cleaved substrate or by luciferase activity induced by the cleaved ATF6 substrate binding to and activating an ATF6 luciferase reporter construct. Using this assay we show that (i) SPP is the first aspartyl intramembrane-cleaving protease whose activity increases proportionally to its overexpression and (ii) selectivity of various SPP and gamma-secretase inhibitors can be rapidly evaluated. Because this assay was designed based on data suggesting that SPP has an orientation distinct from presenilin and cleaves type II membrane proteins, we determined whether the segment of SPP located between the two presumptive catalytic aspartates was in the lumen or cytoplasm. Using site-directed mutagenesis to insert an N-linked glycosylation site we show that a portion of this region is present in the lumen. These data provide strong evidence that although the SPP and presenilin active sites have some similarities, their presumptive catalytic domains are inverted. This assay should prove useful for additional functional studies of SPP as well as evaluation of SPP and gamma-secretase inhibitors.
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Affiliation(s)
- Andrew C Nyborg
- Mayo Clinic, Mayo Clinic College of Medicine, Department of Neuroscience, Jacksonville, Florida 32224, USA
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