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SRPassing Co-translational Targeting: The Role of the Signal Recognition Particle in Protein Targeting and mRNA Protection. Int J Mol Sci 2021; 22:ijms22126284. [PMID: 34208095 PMCID: PMC8230904 DOI: 10.3390/ijms22126284] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2021] [Revised: 06/02/2021] [Accepted: 06/05/2021] [Indexed: 01/13/2023] Open
Abstract
Signal recognition particle (SRP) is an RNA and protein complex that exists in all domains of life. It consists of one protein and one noncoding RNA in some bacteria. It is more complex in eukaryotes and consists of six proteins and one noncoding RNA in mammals. In the eukaryotic cytoplasm, SRP co-translationally targets proteins to the endoplasmic reticulum and prevents misfolding and aggregation of the secretory proteins in the cytoplasm. It was demonstrated recently that SRP also possesses an earlier unknown function, the protection of mRNAs of secretory proteins from degradation. In this review, we analyze the progress in studies of SRPs from different organisms, SRP biogenesis, its structure, and function in protein targeting and mRNA protection.
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2
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Kobayashi K, Jomaa A, Lee JH, Chandrasekar S, Boehringer D, Shan SO, Ban N. Structure of a prehandover mammalian ribosomal SRP·SRP receptor targeting complex. Science 2018; 360:323-327. [PMID: 29567807 PMCID: PMC6309883 DOI: 10.1126/science.aar7924] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2017] [Accepted: 03/12/2018] [Indexed: 01/13/2023]
Abstract
Signal recognition particle (SRP) targets proteins to the endoplasmic reticulum (ER). SRP recognizes the ribosome synthesizing a signal sequence and delivers it to the SRP receptor (SR) on the ER membrane followed by the transfer of the signal sequence to the translocon. Here, we present the cryo-electron microscopy structure of the mammalian translating ribosome in complex with SRP and SR in a conformation preceding signal sequence handover. The structure visualizes all eukaryotic-specific SRP and SR proteins and reveals their roles in stabilizing this conformation by forming a large protein assembly at the distal site of SRP RNA. We provide biochemical evidence that the guanosine triphosphate hydrolysis of SRP·SR is delayed at this stage, possibly to provide a time window for signal sequence handover to the translocon.
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Affiliation(s)
- Kan Kobayashi
- Department of Biology, Institute of Molecular Biology and Biophysics, ETH Zurich, Otto-Stern-Weg 5, Zurich CH-8093, Switzerland
| | - Ahmad Jomaa
- Department of Biology, Institute of Molecular Biology and Biophysics, ETH Zurich, Otto-Stern-Weg 5, Zurich CH-8093, Switzerland
| | - Jae Ho Lee
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Sowmya Chandrasekar
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Daniel Boehringer
- Department of Biology, Institute of Molecular Biology and Biophysics, ETH Zurich, Otto-Stern-Weg 5, Zurich CH-8093, Switzerland
| | - Shu-Ou Shan
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Nenad Ban
- Department of Biology, Institute of Molecular Biology and Biophysics, ETH Zurich, Otto-Stern-Weg 5, Zurich CH-8093, Switzerland.
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3
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Structure and Switch Cycle of SRβ as Ancestral Eukaryotic GTPase Associated with Secretory Membranes. Structure 2015; 23:1838-1847. [PMID: 26299945 DOI: 10.1016/j.str.2015.07.010] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2015] [Revised: 07/15/2015] [Accepted: 07/19/2015] [Indexed: 11/22/2022]
Abstract
G proteins of the Ras-family of small GTPases trace the evolution of eukaryotes. The earliest branching involves the closely related Arf, Sar1, and SRβ GTPases associated with secretory membranes. SRβ is an integral membrane component of the signal recognition particle (SRP) receptor that targets ribosome-nascent chain complexes to the ER. How SRβ integrates into the regulation of SRP-dependent membrane protein biogenesis is not known. Here we show that SRβ-GTP interacts with ribosomes only in presence of SRα and present crystal structures of SRβ in complex with the SRX domain of SRα in the GTP-bound state at 3.2 Å, and of GDP- and GDP · Mg(2+)-bound SRβ at 1.9 Å and 2.4 Å, respectively. We define the GTPase switch cycle of SRβ and identify specific differences to the Arf and Sar1 families with implications for GTPase regulation. Our data allow a better integration of SRβ into the scheme of protein targeting.
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4
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Co-translational targeting and translocation of proteins to the endoplasmic reticulum. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2013; 1833:2392-402. [DOI: 10.1016/j.bbamcr.2013.02.021] [Citation(s) in RCA: 141] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/11/2012] [Revised: 02/18/2013] [Accepted: 02/19/2013] [Indexed: 12/16/2022]
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5
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Abstract
The Signal Recognition Particle (SRP) plays a critical role in the sorting of nascent secretory and membrane proteins. Remarkably, this function has been conserved from bacteria, where SRP delivers proteins to the inner membrane, through to eukaryotes, where SRP is required for targeting of proteins to the endoplasmic reticulum. This review focuses on present understanding of SRP structure and function and the relationship between the two. Furthermore, the similarities and differences in the structure, function and cellular role of SRP in bacteria, chloroplasts, fungi and mammals will be stressed.
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Affiliation(s)
- Martin R Pool
- Faculty of Life Sciences, University of Manchester, Manchester, UK.
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6
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Jiang Y, Cheng Z, Mandon EC, Gilmore R. An interaction between the SRP receptor and the translocon is critical during cotranslational protein translocation. ACTA ACUST UNITED AC 2008; 180:1149-61. [PMID: 18347066 PMCID: PMC2290843 DOI: 10.1083/jcb.200707196] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The signal recognition particle (SRP)-dependent targeting pathway facilitates rapid, efficient delivery of the ribosome-nascent chain complex (RNC) to the protein translocation channel. We test whether the SRP receptor (SR) locates a vacant protein translocation channel by interacting with the yeast Sec61 and Ssh1 translocons. Surprisingly, the slow growth and cotranslational translocation defects caused by deletion of the transmembrane (TM) span of yeast SRbeta (SRbeta-DeltaTM) are exaggerated when the SSH1 gene is disrupted. Disruption of the SBH2 gene, which encodes the beta subunit of the Ssh1p complex, likewise causes a growth defect when combined with SRbeta-DeltaTM. Cotranslational translocation defects in the ssh1DeltaSRbeta-DeltaTM mutant are explained by slow and inefficient in vivo gating of translocons by RNCs. A critical function for translocation channel beta subunits in the SR-channel interaction is supported by the observation that simultaneous deletion of Sbh1p and Sbh2p causes a defect in the cotranslational targeting pathway that is similar to the translocation defect caused by deletion of either subunit of the SR.
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Affiliation(s)
- Ying Jiang
- Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605, USA
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7
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Tuteja R. Unraveling the components of protein translocation pathway in human malaria parasite Plasmodium falciparum. Arch Biochem Biophys 2007; 467:249-60. [PMID: 17919451 DOI: 10.1016/j.abb.2007.08.031] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2007] [Revised: 08/20/2007] [Accepted: 08/22/2007] [Indexed: 10/22/2022]
Abstract
The targeting and translocation of proteins is an essentially required and conserved process in all the living organisms. This complex process involves multiple steps and requires a variety of factors before the protein reaches its final destination. The major components of translocation machinery are signal recognition particle (SRP) and secretory (Sec) complex. These are composed of highly conserved components. SRP contains SRP RNA and other polypeptides such as SRP9, SRP14, SRP19 and SRP54. Sec complex is composed of Sec61alphabetagamma, Sec62 and Sec63. In this review using bioinformatics approach we have shown that the P. falciparum genome contains the homologues for all of these and other factors such as SRP receptor, and TRAM (translocation associated membrane protein), which are required for post- and co-translational protein translocation. We have also shown the various steps of translocation in a hypothetical model.
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Affiliation(s)
- Renu Tuteja
- Malaria Group, International Centre for Genetic Engineering and Biotechnology, P.O. Box 10504, Aruna Asaf Ali Marg, New Delhi 110067, India
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8
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Mitra K, Frank J, Driessen A. Co- and post-translational translocation through the protein-conducting channel: analogous mechanisms at work? Nat Struct Mol Biol 2007; 13:957-64. [PMID: 17082791 DOI: 10.1038/nsmb1166] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Many proteins are translocated across, or integrated into, membranes. Both functions are fulfilled by the 'translocon/translocase', which contains a membrane-embedded protein-conducting channel (PCC) and associated soluble factors that drive translocation and insertion reactions using nucleotide triphosphates as fuel. This perspective focuses on reinterpreting existing experimental data in light of a recently proposed PCC model comprising a front-to-front dimer of SecY or Sec61 heterotrimeric complexes. In this new framework, we propose (i) a revised model for SRP-SR-mediated docking of the ribosome-nascent polypeptide to the PCC; (ii) that the dynamic interplay between protein substrate, soluble factors and PCC controls the opening and closing of a transmembrane channel across, and/or a lateral gate into, the membrane; and (iii) that co- and post-translational translocation, involving the ribosome and SecA, respectively, not only converge at the PCC but also use analogous mechanisms for coordinating protein translocation.
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9
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Halic M, Gartmann M, Schlenker O, Mielke T, Pool MR, Sinning I, Beckmann R. Signal recognition particle receptor exposes the ribosomal translocon binding site. Science 2006; 312:745-7. [PMID: 16675701 DOI: 10.1126/science.1124864] [Citation(s) in RCA: 123] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Signal sequences of secretory and membrane proteins are recognized by the signal recognition particle (SRP) as they emerge from the ribosome. This results in their targeting to the membrane by docking with the SRP receptor, which facilitates transfer of the ribosome to the translocon. Here, we present the 8 angstrom cryo-electron microscopy structure of a "docking complex" consisting of a SRP-bound 80S ribosome and the SRP receptor. Interaction of the SRP receptor with both SRP and the ribosome rearranged the S domain of SRP such that a ribosomal binding site for the translocon, the L23e/L35 site, became exposed, whereas Alu domain-mediated elongation arrest persisted.
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Affiliation(s)
- Mario Halic
- Institute of Biochemistry, Charité, University Medical School Berlin, Monbijoustrasse 2, 10117 Berlin, Germany
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10
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Schlenker O, Hendricks A, Sinning I, Wild K. The structure of the mammalian signal recognition particle (SRP) receptor as prototype for the interaction of small GTPases with Longin domains. J Biol Chem 2006; 281:8898-906. [PMID: 16439358 DOI: 10.1074/jbc.m512415200] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
The eukaryotic signal recognition particle (SRP) and its receptor (SR) play a central role in co-translational targeting of secretory and membrane proteins to the endoplasmic reticulum. The SR is a heterodimeric complex assembled by the two GTPases SRalpha and SRbeta, which is membrane-anchored. Here we present the 2.45-A structure of mammalian SRbeta in its Mg2+ GTP-bound state in complex with the minimal binding domain of SRalpha termed SRX. SRbeta is a member of the Ras-GTPase superfamily closely related to Arf and Sar1, while SRX belongs to the SNARE-like superfamily with a fold also known as longin domain. SRX binds to the P loop and the switch regions of SRbeta-GTP. The binding mode and structural similarity with other GTPase-effector complexes suggests a co-GAP (GTPase-activating protein) function for SRX. Comparison with the homologous yeast structure and other longin domains reveals a conserved adjustable hydrophobic surface within SRX which is of central importance for the SRbeta-GTP:SRX interface. A helix swap in SRX results in the formation of a dimer in the crystal structure. Based on structural conservation we present the SRbeta-GTP:SRX structure as a prototype for conserved interactions in a variety of GTPase regulated targeting events occurring at endomembranes.
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Affiliation(s)
- Oliver Schlenker
- Biochemie-Zentrum der Universität Heidelberg (BZH), Im Neuenheimer Feld 328, D-69120 Heidelberg, Germany
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11
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Abrams EW, Andrew DJ. CrebA regulates secretory activity in theDrosophilasalivary gland and epidermis. Development 2005; 132:2743-58. [PMID: 15901661 DOI: 10.1242/dev.01863] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Understanding how organs acquire the capacity to perform their respective functions is important for both cell and developmental biology. Here, we have examined the role of early-expressed transcription factors in activating genes crucial for secretory function in the Drosophila salivary gland. We show that expression of genes encoding proteins required for ER targeting and translocation, and proteins that mediate transport between the ER and Golgi is very high in the early salivary gland. This high level expression requires two early salivary gland transcription factors; CrebA is required throughout embryogenesis and Fkh is required only during late embryonic stages. As Fkh is required to maintain late CrebA expression in the salivary gland, Fkh probably works through CrebA to affect secretory pathway gene expression. In support of these regulatory interactions, we show that CrebA is important for elevated secretion in the salivary gland. Additionally, CrebA is required for the expression of the secretory pathway genes in the embryonic epidermis, where CrebA had previously been shown to be essential for cuticle development. We show that zygotic mutations in several individual secretory pathway genes result in larval cuticle phenotypes nearly identical to those of CrebA mutants. Thus, CrebA activity is linked to secretory function in multiple tissues.
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Affiliation(s)
- Elliott W Abrams
- Department of Cell Biology, The Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, MD 21205, USA
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12
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Abstract
The signal recognition particle (SRP) directs integral membrane and secretory proteins to the cellular protein translocation machinery during translation. The SRP is an evolutionarily conserved RNA-protein complex whose activities are regulated by GTP hydrolysis. Recent structural investigations of SRP functional domains and interactions provide new insights into the mechanisms of SRP activity in all cells, leading toward a comprehensive understanding of protein trafficking by this elegant pathway.
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Affiliation(s)
- Jennifer A Doudna
- Department of Molecular and Cell Biology, Howard Hughes Medical Institute, University of California at Berkeley, Berkeley, California 94705, USA.
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13
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Song BD, Leonard M, Schmid SL. Dynamin GTPase domain mutants that differentially affect GTP binding, GTP hydrolysis, and clathrin-mediated endocytosis. J Biol Chem 2004; 279:40431-6. [PMID: 15262989 DOI: 10.1074/jbc.m407007200] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The GTPase dynamin is essential for clathrin-mediated endocytosis. Unlike most GTPases, dynamin has a low affinity for nucleotide, a high rate of GTP hydrolysis, and can self-assemble, forming higher order structures such as rings and spirals that exhibit up to 100-fold stimulated GTPase activity. The role(s) of GTP binding and/or hydrolysis in endocytosis remain unclear because mutations in the GTPase domain so far studied impair both. We generated a new series of GTPase domain mutants to probe the mechanism of GTP hydrolysis and to further test the role of GTP binding and/or hydrolysis in endocytosis. Each of the mutations had parallel effects on assembly-stimulated and basal GTPase activities. In contrast to previous reports, we find that mutation of Thr-65 to Ala (or Asp or His) dramatically lowered both the rate of assembly-stimulated GTP hydrolysis and the affinity for GTP. The assemblystimulated rate of hydrolysis was lowered by the mutation of Ser-61 to Asp and increased by the mutation of Thr-141 to Ala without significantly altering the Km for GTP. For some mutants and to a lesser extent for WT dynamin, self-assembly dramatically altered the Km for GTP, suggesting that conformational changes in the active site accompany self-assembly. Analysis of transferrin endocytosis rates in cells overexpressing mutant dynamins revealed a stronger correlation with both the basal and assembly-stimulated rates of GTP hydrolysis than with the calculated ratio of dynamin-GTP/free dynamin, suggesting that GTP binding is not sufficient, and GTP hydrolysis is required for clathrin-mediated endocytosis in vivo.
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Affiliation(s)
- Byeong Doo Song
- Department of Cell Biology, The Scripps Research Institute, La Jolla, California 92037, USA
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14
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Mandon EC, Jiang Y, Gilmore R. Dual recognition of the ribosome and the signal recognition particle by the SRP receptor during protein targeting to the endoplasmic reticulum. J Cell Biol 2003; 162:575-85. [PMID: 12913112 PMCID: PMC2173783 DOI: 10.1083/jcb.200303143] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We have analyzed the interactions between the signal recognition particle (SRP), the SRP receptor (SR), and the ribosome using GTPase assays, biosensor experiments, and ribosome binding assays. Possible mechanisms that could contribute to an enhanced affinity between the SR and the SRP-ribosome nascent chain complex to promote protein translocation under physiological ionic strength conditions have been explored. Ribosomes or 60S large ribosomal subunits activate the GTPase cycle of SRP54 and SRalpha by providing a platform for assembly of the SRP-SR complex. Biosensor experiments revealed high-affinity, saturable binding of ribosomes or large ribosomal subunits to the SR. Remarkably, the SR has a 100-fold higher affinity for the ribosome than for SRP. Proteoliposomes that contain the SR bind nontranslating ribosomes with an affinity comparable to that shown by the Sec61 complex. An NH2-terminal 319-residue segment of SRalpha is necessary and sufficient for binding of SR to the ribosome. We propose that the ribosome-SR interaction accelerates targeting of the ribosome nascent chain complex to the RER, while the SRP-SR interaction is crucial for maintaining the fidelity of the targeting reaction.
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Affiliation(s)
- Elisabet C Mandon
- Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, 364 Plantation Street, Worcester, MA 01605-2324, USA
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15
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Legate KR, Andrews DW. The beta-subunit of the signal recognition particle receptor is a novel GTP-binding protein without intrinsic GTPase activity. J Biol Chem 2003; 278:27712-20. [PMID: 12759365 DOI: 10.1074/jbc.m302158200] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The beta-subunit of the signal recognition particle receptor (SRbeta), a member of the Ras family of small molecular weight GTPases, is involved in the targeting of nascent polypeptide chains to the protein translocation machinery in the endoplasmic reticulum membrane. We purified SRbeta from an expressing strain of Escherichia coli and investigated the properties of the isolated GTPase. We find that, unlike other Ras family GTPases, most SRbeta purifies bound to GTP, and SRbeta-bound GTP is not easily exchanged with solution GTP. SRbeta possesses no detectable GTPase activity. Although a stable interaction between SRbeta and ribosomes is observed, SRbeta is not stimulated to hydrolyze GTP when incubated with ribosomes or ribosome-nascent chains. A GTPase mutant harboring a mutation in a region predicted to be functionally important, based on observations made in related GTPases, binds GTP with faster kinetics and appears to be a less stable protein but otherwise displays similar properties to the wild-type SRbeta GTPase. Our results demonstrate that as an isolated GTPase, SRbeta functions differently from the Arf- and Ras-type GTPases that it is most closely related to by sequence.
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MESH Headings
- Animals
- Chromatography, High Pressure Liquid
- Cross-Linking Reagents/pharmacology
- DNA, Complementary/metabolism
- Dose-Response Relationship, Drug
- Endoplasmic Reticulum/metabolism
- Escherichia coli/metabolism
- GTP Phosphohydrolases/metabolism
- GTP-Binding Proteins/metabolism
- Guanosine Triphosphate/metabolism
- Humans
- Hydrolysis
- Intracellular Membranes/metabolism
- Kinetics
- Mutagenesis, Site-Directed
- Mutation
- Plasmids/metabolism
- Precipitin Tests
- Protein Binding
- Protein Structure, Tertiary
- Receptors, Cytoplasmic and Nuclear/chemistry
- Receptors, Cytoplasmic and Nuclear/physiology
- Receptors, Peptide/chemistry
- Receptors, Peptide/physiology
- Ribosomes/metabolism
- Saccharomyces cerevisiae/metabolism
- Spectrometry, Fluorescence
- Time Factors
- Ultraviolet Rays
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Affiliation(s)
- Kyle R Legate
- Department of Biochemistry, McMaster University, Hamilton, Ontario L8N 3Z5, Canada
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16
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Koch HG, Moser M, Müller M. Signal recognition particle-dependent protein targeting, universal to all kingdoms of life. Rev Physiol Biochem Pharmacol 2003; 146:55-94. [PMID: 12605305 DOI: 10.1007/s10254-002-0002-9] [Citation(s) in RCA: 114] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
Abstract
The signal recognition particle (SRP) and its membrane-bound receptor represent a ubiquitous protein-targeting device utilized by organisms as different as bacteria and humans, archaea and plants. The unifying concept of SRP-dependent protein targeting is that SRP binds to signal sequences of newly synthesized proteins as they emerge from the ribosome. In eukaryotes this interaction arrests or retards translation elongation until SRP targets the ribosome-nascent chain complexes via the SRP receptor to the translocation channel. Such channels are present in the endoplasmic reticulum of eukaryotic cells, the thylakoids of chloroplasts, or the plasma membrane of prokaryotes. The minimal functional unit of SRP consists of a signal sequence-recognizing protein and a small RNA. The as yet most complex version is the mammalian SRP whose RNA, together with six proteinaceous subunits, undergo an intricate assembly process. The preferential substrates of SRP possess especially hydrophobic signal sequences. Interactions between SRP and its receptor, the ribosome, the signal sequence, and the target membrane are regulated by GTP hydrolysis. SRP-dependent protein targeting in bacteria and chloroplasts slightly deviate from the canonical mechanism found in eukaryotes. Pro- and eukaryotic cells harbour regulatory mechanisms to prevent a malfunction of the SRP pathway.
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Affiliation(s)
- H-G Koch
- Institut für Biochemie und Molekularbiologie, Universität Freiburg, Hermann-Herder-Strasse 7, 79104, Freiburg, Germany.
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17
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Schwartz T, Blobel G. Structural basis for the function of the beta subunit of the eukaryotic signal recognition particle receptor. Cell 2003; 112:793-803. [PMID: 12654246 DOI: 10.1016/s0092-8674(03)00161-2] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Protein translocation across and insertion into membranes is a process essential to all life forms. In higher eukaryotes, this process is initiated by targeting the translating ribosome to the endoplasmic reticulum via the signal recognition particle (SRP) and its membrane-associated heterodimeric receptor (SR). This targeting step is regulated by three G proteins, SRP54, SR alpha, and SR beta, which act in concert. Little is known about the regulatory role of SR beta. Here, we present the 1.7 A crystal structure of the SR beta-GTP subunit in complex with the interaction domain of SR alpha. Strikingly, the binding interface overlaps largely with the switch 1 region of SR beta. This finding, together with additional biochemical data, shows that the eukaryotic SR is a conditional and not an obligate heterodimer. The results suggest that the GTP/GDP switch cycle of SR beta functions as a regulatory switch for the receptor dimerization. We discuss the implications for the translocation pathway.
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Affiliation(s)
- Thomas Schwartz
- Howard Hughes Medical Institute, Laboratory of Cell Biology, The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA
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18
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Abstract
The signal recognition particle (SRP) and its membrane-associated receptor (SR) catalyze targeting of nascent secretory and membrane proteins to the protein translocation apparatus of the cell. Components of the SRP pathway and salient features of the molecular mechanism of SRP-dependent protein targeting are conserved in all three kingdoms of life. Recent advances in the structure determination of a number of key components in the eukaryotic and prokaryotic SRP pathway provide new insight into the molecular basis of SRP function, and they set the stage for future work toward an integrated picture that takes into account the dynamic and contextual properties of this remarkable cellular machine.
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Affiliation(s)
- R J Keenan
- Maxygen, 515 Galveston Drive, Redwood City, California 94063, USA.
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19
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Millman JS, Qi HY, Vulcu F, Bernstein HD, Andrews DW. FtsY binds to the Escherichia coli inner membrane via interactions with phosphatidylethanolamine and membrane proteins. J Biol Chem 2001; 276:25982-9. [PMID: 11353766 DOI: 10.1074/jbc.m011331200] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Targeting of many polytopic proteins to the inner membrane of prokaryotes occurs via an essential signal recognition particle-like pathway. FtsY, the Escherichia coli homolog of the eukaryotic signal recognition particle receptor alpha-subunit, binds to membranes via its amino-terminal AN domain. We demonstrate that FtsY assembles on membranes via interactions with phosphatidylethanolamine and with a trypsin-sensitive component. Both interactions are mediated by the AN domain of FtsY. In the absence of phosphatidylethanolamine, the trypsin-sensitive component is sufficient for binding and function of FtsY in the targeting of membrane proteins. We propose a two-step mechanism for the assembly of FtsY on the membrane similar to that of SecA on the E. coli inner membrane.
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Affiliation(s)
- J S Millman
- Department of Biochemistry, McMaster University, Hamilton, Ontario L8N 3Z5, Canada
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20
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Abstract
It is becoming increasingly clear that similarities exist in the manner in which extracytoplasmic proteins are targeted to complexes responsible for translocating these proteins across membranes in each of the three domains of life. In Eukarya and Bacteria, the signal recognition particle (SRP) directs nascent polypeptides to membrane-embedded translocation sites. In Archaea, the SRP protein targeting pathway apparently represents an intermediate between the bacterial and eukaryal systems. Understanding the archaeal SRP pathway could therefore reveal universal aspects of targeting not detected in current comparisons of the eukaryal and bacterial systems while possibly identifying aspects of the process either not previously reported or unique to Archaea.
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Affiliation(s)
- J Eichler
- Department of Life Sciences, Ben Gurion University, PO Box 653, Beersheva 84105, Israel.
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21
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Herskovits AA, Bochkareva ES, Bibi E. New prospects in studying the bacterial signal recognition particle pathway. Mol Microbiol 2000; 38:927-39. [PMID: 11123669 DOI: 10.1046/j.1365-2958.2000.02198.x] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In vivo and in vitro studies have suggested that the bacterial version of the mammalian signal recognition particle (SRP) system plays an essential and selective role in protein biogenesis. The bacterial SRP system consists of at least two proteins and an RNA molecule (termed Ffh, FtsY and 4.5S RNA, respectively, in Escherichia coli). Recent evidence suggests that other putative bacterial-specific SRP components may also exist. In vitro experiments confirmed the expected basic features of the bacterial SRP system by demonstrating interactions among the SRP components themselves, between them and ribosomes, ribosome-linked hydrophobic nascent polypeptides or inner membranes. The availability of a conserved (and essential) bacterial SRP version has facilitated the implementation of powerful genetic and biochemical approaches for studying the cascade of events during the SRP-mediated targeting process in vivo and in vitro as well as the three-dimensional structures and the properties of each SRP component and complex.
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Affiliation(s)
- A A Herskovits
- Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel
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