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.

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.

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 NAC functions as a modulator of SRP during the early steps of protein targeting to the endoplasmic reticulum

2012 ◽  
Vol 23 (16) ◽  
pp. 3027-3040 ◽  
Author(s):  
Ying Zhang ◽  
Uta Berndt ◽  
Hanna Gölz ◽  
Arlette Tais ◽  
Stefan Oellerer ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Targeting ◽  
Signal Sequence ◽  
Signal Recognition Particle ◽  
Signal Recognition ◽  
Signal Sequences ◽  
Chain Complexes ◽  
Ribosomal Tunnel ◽  
Nascent Chain ◽  
Combined Data

Nascent polypeptide-associated complex (NAC) was initially found to bind to any segment of the nascent chain except signal sequences. In this way, NAC is believed to prevent mistargeting due to binding of signal recognition particle (SRP) to signalless ribosome nascent chain complexes (RNCs). Here we revisit the interplay between NAC and SRP. NAC does not affect SRP function with respect to signalless RNCs; however, NAC does affect SRP function with respect to RNCs targeted to the endoplasmic reticulum (ER). First, early recruitment of SRP to RNCs containing a signal sequence within the ribosomal tunnel is NAC dependent. Second, NAC is able to directly and tightly bind to nascent signal sequences. Third, SRP initially displaces NAC from RNCs; however, when the signal sequence emerges further, trimeric NAC·RNC·SRP complexes form. Fourth, upon docking to the ER membrane NAC remains bound to RNCs, allowing NAC to shield cytosolically exposed nascent chain domains not only before but also during cotranslational translocation. The combined data indicate a functional interplay between NAC and SRP on ER-targeted RNCs, which is based on the ability of the two complexes to bind simultaneously to distinct segments of a single nascent chain.

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 SRPassing Co-translational Targeting: The Role of the Signal Recognition Particle in Protein Targeting and mRNA Protection

2021 ◽  
Vol 22 (12) ◽  
pp. 6284
Author(s):  
Morgana K. Kellogg ◽  
Sarah C. Miller ◽  
Elena B. Tikhonova ◽  
Andrey L. Karamyshev
Keyword(s):  
Endoplasmic Reticulum ◽  
Noncoding Rna ◽  
Protein Targeting ◽  
Signal Recognition Particle ◽  
Structure And Function ◽  
Secretory Proteins ◽  
Signal Recognition ◽  
Domains Of Life ◽  
And Function

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.

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 The beta subunit of the signal recognition particle receptor is a transmembrane GTPase that anchors the alpha subunit, a peripheral membrane GTPase, to the endoplasmic reticulum membrane.

1995 ◽  
Vol 128 (3) ◽  
pp. 273-282 ◽  
Author(s):  
J D Miller ◽  
S Tajima ◽  
L Lauffer ◽  
P Walter
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Targeting ◽  
Signal Sequence ◽  
Transmembrane Protein ◽  
Signal Recognition Particle ◽  
Endoplasmic Reticulum Membrane ◽  
Protein Chain ◽  
Signal Recognition ◽  
Signal Recognition Particle Receptor ◽  
Er Membrane

The signal recognition particle receptor (SR) is required for the cotranslational targeting of both secretory and membrane proteins to the endoplasmic reticulum (ER) membrane. During targeting, the SR interacts with the signal recognition particle (SRP) which is bound to the signal sequence of the nascent protein chain. This interaction catalyzes the GTP-dependent transfer of the nascent chain from SRP to the protein translocation apparatus in the ER membrane. The SR is a heterodimeric protein comprised of a 69-kD subunit (SR alpha) and a 30-kD subunit (SR beta) which are associated with the ER membrane in an unknown manner. SR alpha and the 54-kD subunits of SRP (SRP54) each contain related GTPase domains which are required for SR and SRP function. Molecular cloning and sequencing of a cDNA encoding SR beta revealed that SR beta is a transmembrane protein and, like SR alpha and SRP54, is a member of the GTPase superfamily. Although SR beta defines its own GTPase subfamily, it is distantly related to ARF and Sar1. Using UV cross-linking, we confirm that SR beta binds GTP specifically. Proteolytic digestion experiments show that SR alpha is required for the interaction of SRP with SR. SR alpha appears to be peripherally associated with the ER membrane, and we suggest that SR beta, as an integral membrane protein, mediates the membrane association of SR alpha. The discovery of its guanine nucleotide-binding domain, however, makes it likely that its role is more complex than that of a passive anchor for SR alpha. These findings suggest that a cascade of three directly interacting GTPases functions during protein targeting to the ER membrane.

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