scholarly journals Getting on target: The archaeal signal recognition particle

Archaea ◽  
2002 ◽  
Vol 1 (1) ◽  
pp. 27-34 ◽  
Author(s):  
Christian Zwieb ◽  
Jerry Eichler
Keyword(s):  
Membrane Proteins ◽  
Biochemical Analysis ◽  
Protein Targeting ◽  
Polypeptide Chain ◽  
Protein Translocation ◽  
Signal Recognition Particle ◽  
Evolutionary Significance ◽  
Signal Recognition ◽  
Functional Behavior ◽  
Translocation Pathway

Protein translocation begins with the efficient targeting of secreted and membrane proteins to complexes embedded within the membrane. In Eukarya and Bacteria, this is achieved through the interaction of the signal recognition particle (SRP) with the nascent polypeptide chain. In Archaea, homologs of eukaryal and bacterial SRP-mediated translocation pathway components have been identified. Biochemical analysis has revealed that although the archaeal system incorporates various facets of the eukaryal and bacterial targeting systems, numerous aspects of the archaeal system are unique to this domain of life. Moreover, it is becoming increasingly clear that elucidation of the archaeal SRP pathway will provide answers to basic questions about protein targeting that cannot be obtained from examination of eukaryal or bacterial models. In this review, recent data regarding the molecular composition, functional behavior and evolutionary significance of the archaeal signal recognition particle pathway are discussed.

scholarly journals Emerging View on the Molecular Functions of Sec62 and Sec63 in Protein Translocation

2021 ◽  
Vol 22 (23) ◽  
pp. 12757
Author(s):  
Sung-jun Jung ◽  
Hyun Kim
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Targeting ◽  
Protein Translocation ◽  
Signal Recognition Particle ◽  
Signal Recognition ◽  
Conducting Channel ◽  
Evolutionarily Conserved ◽  
Translocation Pathway ◽  
Molecular Functions ◽  
Sec61 Channel

Most secreted and membrane proteins are targeted to and translocated across the endoplasmic reticulum (ER) membrane through the Sec61 protein-conducting channel. Evolutionarily conserved Sec62 and Sec63 associate with the Sec61 channel, forming the Sec complex and mediating translocation of a subset of proteins. For the last three decades, it has been thought that ER protein targeting and translocation occur via two distinct pathways: signal recognition particle (SRP)-dependent co-translational or SRP-independent, Sec62/Sec63 dependent post-translational translocation pathway. However, recent studies have suggested that ER protein targeting and translocation through the Sec translocon are more intricate than previously thought. This review summarizes the current understanding of the molecular functions of Sec62/Sec63 in ER protein translocation.

SRP RNA Remodeling by SRP68 Explains Its Role in Protein Translocation

Science ◽  
2014 ◽  
Vol 344 (6179) ◽  
pp. 101-104 ◽  
Author(s):  
Jan Timo Grotwinkel ◽  
Klemens Wild ◽  
Bernd Segnitz ◽  
Irmgard Sinning
Keyword(s):  
Ribosomal Rna ◽  
Protein Targeting ◽  
Rna Binding ◽  
Protein Translocation ◽  
Signal Recognition Particle ◽  
Structural Basis ◽  
Signal Recognition ◽  
Rna Remodeling ◽  
Srp Rna ◽  
Arginine Rich Motif

The signal recognition particle (SRP) is central to membrane protein targeting; SRP RNA is essential for SRP assembly, elongation arrest, and activation of SRP guanosine triphosphatases. In eukaryotes, SRP function relies on the SRP68-SRP72 heterodimer. We present the crystal structures of the RNA-binding domain of SRP68 (SRP68-RBD) alone and in complex with SRP RNA and SRP19. SRP68-RBD is a tetratricopeptide-like module that binds to a RNA three-way junction, bends the RNA, and inserts an α-helical arginine-rich motif (ARM) into the major groove. The ARM opens the conserved 5f RNA loop, which in ribosome-bound SRP establishes a contact to ribosomal RNA. Our data provide the structural basis for eukaryote-specific, SRP68-driven RNA remodeling required for protein translocation.

scholarly journals In Vivo Analysis of an Essential Archaeal Signal Recognition Particle in Its Native Host

2002 ◽  
Vol 184 (12) ◽  
pp. 3260-3267 ◽  
Author(s):  
R. Wesley Rose ◽  
Mechthild Pohlschröder
Keyword(s):  
Protein Targeting ◽  
Protein Translocation ◽  
Signal Recognition Particle ◽  
Signal Recognition ◽  
Sequence Comparisons ◽  
Protein Insertion ◽  
Native Host

ABSTRACT The evolutionarily conserved signal recognition particle (SRP) plays an integral role in Sec-mediated cotranslational protein translocation and membrane protein insertion, as it has been shown to target nascent secretory and membrane proteins to the bacterial and eukaryotic translocation pores. However, little is known about its function in archaea, since characterization of the SRP in this domain of life has thus far been limited to in vitro reconstitution studies of heterologously expressed archaeal SRP components identified by sequence comparisons. In the present study, the genes encoding the SRP54, SRP19, and 7S RNA homologs (hv54h, hv19h, and hv7Sh, respectively) of the genetically and biochemically tractable archaeon Haloferax volcanii were cloned, providing the tools to analyze the SRP in its native host. As part of this analysis, an hv54h knockout strain was created. In vivo characterization of this strain revealed that the archaeal SRP is required for viability, suggesting that cotranslational protein translocation is an essential process in archaea. Furthermore, a method for the purification of this SRP employing nickel chromatography was developed in H. volcanii, allowing the successful copurification of (i) Hv7Sh with a histidine-tagged Hv54h, as well as (ii) Hv54h and Hv7Sh with a histidine-tagged Hv19h. These results provide the first in vivo evidence that these components interact in archaea. Such copurification studies will provide insight into the significance of the similarities and differences of the protein-targeting systems of the three domains of life, thereby increasing knowledge about the recognition of translocated proteins in general.

scholarly journals Conformational changes in the GTPase modules of the signal reception particle and its receptor drive initiation of protein translocation

2007 ◽  
Vol 178 (4) ◽  
pp. 611-620 ◽  
Author(s):  
Shu-ou Shan ◽  
Sowmya Chandrasekar ◽  
Peter Walter
Keyword(s):  
Conformational Changes ◽  
Protein Targeting ◽  
Protein Translocation ◽  
Signal Recognition Particle ◽  
Signal Recognition ◽  
Gtp Hydrolysis ◽  
Translocation Efficiency ◽  
Cargo Proteins ◽  
Gtpase Activation ◽  
Guanosine Triphosphatase

During cotranslational protein targeting, two guanosine triphosphatase (GTPase) in the signal recognition particle (SRP) and its receptor (SR) form a unique complex in which hydrolyses of both guanosine triphosphates (GTP) are activated in a shared active site. It was thought that GTP hydrolysis drives the recycling of SRP and SR, but is not crucial for protein targeting. Here, we examined the translocation efficiency of mutant GTPases that block the interaction between SRP and SR at specific stages. Surprisingly, mutants that allow SRP–SR complex assembly but block GTPase activation severely compromise protein translocation. These mutations map to the highly conserved insertion box domain loops that rearrange upon complex formation to form multiple catalytic interactions with the two GTPs. Thus, although GTP hydrolysis is not required, the molecular rearrangements that lead to GTPase activation are essential for protein targeting. Most importantly, our results show that an elaborate rearrangement within the SRP–SR GTPase complex is required to drive the unloading and initiate translocation of cargo proteins.

scholarly journals Compensating complete loss of signal recognition particle during co-translational protein targeting by the translation speed and accuracy

2021 ◽  
Author(s):  
Liuqun Zhao ◽  
Gang Fu ◽  
Yanyan Cui ◽  
Zixiang Xu ◽  
Dawei Zhang
Keyword(s):  
Membrane Proteins ◽  
Protein Targeting ◽  
Time Window ◽  
Signal Recognition Particle ◽  
Protein Translation ◽  
Suppressor Mutation ◽  
Signal Recognition ◽  
Translation Rate ◽  
Inner Membrane ◽  
Speed And Accuracy

Signal recognition particle (SRP) is critical for delivering co-translational proteins to the bacterial inner membrane. Previously, we identified SRP suppressors in Escherichia coli that inhibit translation initiation and elongation, which provides an insight into the mechanism of bypassing the requirement of SRP. Suppressor mutations tend to be located in regions that govern protein translation under evolutionary pressure. To verify this hypothesis, we re-executed the suppressor screening of SRP. Here we isolated a novel SRP suppressor mutation located in the Shine-Dalgarno sequence of S10 operon, which partially offset the targeting defects of SRP-dependent proteins. We found that the suppressor mutation slowed the translation rate of proteins, especially of inner membrane proteins, which could compensate for the targeting defects of inner membrane proteins via extending the time window of protein targeting. Furthermore, the fidelity of translation was decreased in suppressor cells, suggesting that the quality control of translation was inactivated to provide a survival advantage under the loss of SRP stress. Our results demonstrate that the inefficient protein targeting due to SRP deletion can be rescued through modulating translational speed and accuracy.

scholarly journals Receptor compaction and GTPase movements drive cotranslational protein translocation

2020 ◽  
Author(s):  
Jae Ho Lee ◽  
SangYoon Chung ◽  
Yu-Hsien Hwang Fu ◽  
Ruilin Qian ◽  
Xuemeng Sun ◽  
...  
Keyword(s):  
Single Molecule ◽  
Protein Targeting ◽  
Protein Translocation ◽  
Signal Sequence ◽  
Signal Recognition Particle ◽  
Signal Recognition ◽  
Biological Regulation ◽  
Single Molecule Fluorescence Spectroscopy ◽  
Cause Of Failure ◽  
Distal Site

AbstractSignal recognition particle (SRP) is a universally conserved targeting machine that couples the synthesis of ~30% of the proteome to their proper membrane localization1,2. In eukaryotic cells, SRP recognizes translating ribosomes bearing hydrophobic signal sequences and, through interaction with SRP receptor (SR), delivers them to the Sec61p translocase on the endoplasmic reticulum (ER) membrane1,2. How SRP ensures efficient and productive initiation of protein translocation at the ER is not well understood. Here, single molecule fluorescence spectroscopy demonstrates that cargo-loaded SRP induces a global compaction of SR, driving a >90 Å movement of the SRP•SR GTPase complex from the vicinity of the ribosome exit, where it initially assembles, to the distal site of SRP. These rearrangements bring translating ribosomes near the membrane, expose conserved Sec61p docking sites on the ribosome and weaken SRP’s interaction with the signal sequence on the nascent polypeptide, thus priming the translating ribosome for engaging the translocation machinery. Disruption of these rearrangements severely impairs cotranslational protein translocation and is the cause of failure in an SRP54 mutant linked to severe congenital neutropenia. Our results demonstrate that multiple largescale molecular motions in the SRP•SR complex are required to drive the transition from protein targeting to translocation; these post-targeting rearrangements provide potential new points for biological regulation as well as disease intervention.

scholarly journals Down-Regulation of the Trypanosomatid Signal Recognition Particle Affects the Biogenesis of Polytopic Membrane Proteins but Not of Signal Peptide-Containing Proteins

2007 ◽  
Vol 6 (10) ◽  
pp. 1865-1875 ◽  
Author(s):  
Yaniv Lustig ◽  
Yaron Vagima ◽  
Hanoch Goldshmidt ◽  
Avigail Erlanger ◽  
Vered Ozeri ◽  
...  
Keyword(s):  
Membrane Proteins ◽  
Signal Peptide ◽  
Mammalian Cells ◽  
Fluorescent Protein ◽  
Protein Translocation ◽  
Signal Recognition Particle ◽  
Dominant Negative ◽  
Signal Recognition ◽  
Rnai Silencing ◽  
7Sl Rna

ABSTRACT Protein translocation across the endoplasmic reticulum is mediated by the signal recognition particle (SRP). In this study, the SRP pathway in trypanosomatids was down-regulated by two approaches: RNA interference (RNAi) silencing of genes encoding SRP proteins in Trypanosoma brucei and overexpression of dominant-negative mutants of 7SL RNA in Leptomonas collosoma. The biogenesis of both signal peptide-containing proteins and polytopic membrane proteins was examined using endogenous and green fluorescent protein-fused proteins. RNAi silencing of SRP54 or SRP68 in T. brucei resulted in reduced levels of polytopic membrane proteins, but no effect on the level of signal peptide-containing proteins was observed. When SRP deficiency was achieved in L. collosoma by overexpression of dominant-negative mutated 7SL RNA, a major effect was observed on polytopic membrane proteins but not on signal peptide-containing proteins. This study included two trypanosomatid species, tested various protein substrates, and induced depletion of the SRP pathway by affecting either the levels of SRP binding proteins or that of SRP RNA. Our results demonstrate that, as in bacteria but in contrast to mammalian cells, the trypanosome SRP is mostly essential for the biogenesis of membrane proteins.

scholarly journals A functional link between the co-translational protein translocation pathway and the UPR

eLife ◽  
2015 ◽  
Vol 4 ◽  
Author(s):  
Rachel Plumb ◽  
Zai-Rong Zhang ◽  
Suhila Appathurai ◽  
Malaiyalam Mariappan
Keyword(s):  
Transmembrane Domain ◽  
Protein Translocation ◽  
Signal Recognition Particle ◽  
Signal Recognition ◽  
Functional Link ◽  
Unfolded Protein ◽  
Nascent Chain ◽  
Translocation Pathway ◽  
The Unfolded Protein Response ◽  
Protein Response

Upon endoplasmic reticulum (ER) stress, the transmembrane endoribonuclease Ire1α performs mRNA cleavage reactions to increase the ER folding capacity. It is unclear how the low abundant Ire1α efficiently finds and cleaves the majority of mRNAs at the ER membrane. Here, we reveal that Ire1α forms a complex with the Sec61 translocon to cleave its mRNA substrates. We show that Ire1α's key substrate, XBP1u mRNA, is recruited to the Ire1α-Sec61 translocon complex through its nascent chain, which contains a pseudo-transmembrane domain to utilize the signal recognition particle (SRP)-mediated pathway. Depletion of SRP, the SRP receptor or the Sec61 translocon in cells leads to reduced Ire1α-mediated splicing of XBP1u mRNA. Furthermore, mutations in Ire1α that disrupt the Ire1α-Sec61 complex causes reduced Ire1α-mediated cleavage of ER-targeted mRNAs. Thus, our data suggest that the Unfolded Protein Response is coupled with the co-translational protein translocation pathway to maintain protein homeostasis in the ER during stress conditions.

scholarly journals Dual recognition of the ribosome and the signal recognition particle by the SRP receptor during protein targeting to the endoplasmic reticulum

2003 ◽  
Vol 162 (4) ◽  
pp. 575-585 ◽  
Author(s):  
Elisabet C. Mandon ◽  
Ying Jiang ◽  
Reid Gilmore
Keyword(s):  
Protein Targeting ◽  
Protein Translocation ◽  
Signal Recognition Particle ◽  
Chain Complex ◽  
Signal Recognition ◽  
Binding Assays ◽  
Ribosomal Subunits ◽  
Nascent Chain ◽  
Gtpase Cycle ◽  
Necessary And Sufficient

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 SRα 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 SRα 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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