scholarly journals Lipid activation of the signal recognition particle receptor provides spatial coordination of protein targeting

2010 ◽  
Vol 190 (4) ◽  
pp. 623-635 ◽  
Author(s):  
Vinh Q. Lam ◽  
David Akopian ◽  
Michael Rome ◽  
Doug Henningsen ◽  
Shu-ou Shan
Keyword(s):  
Conformational Changes ◽  
Protein Targeting ◽  
Signal Recognition Particle ◽  
Lipid Binding ◽  
Signal Recognition ◽  
Complex Assembly ◽  
Spatial Coordination ◽  
Cargo Proteins ◽  
Target Membrane ◽  
Cellular Machinery

The signal recognition particle (SRP) and SRP receptor comprise the major cellular machinery that mediates the cotranslational targeting of proteins to cellular membranes. It remains unclear how the delivery of cargos to the target membrane is spatially coordinated. We show here that phospholipid binding drives important conformational rearrangements that activate the bacterial SRP receptor FtsY and the SRP–FtsY complex. This leads to accelerated SRP–FtsY complex assembly, and allows the SRP–FtsY complex to more efficiently unload cargo proteins. Likewise, formation of an active SRP–FtsY GTPase complex exposes FtsY’s lipid-binding helix and enables stable membrane association of the targeting complex. Thus, membrane binding, complex assembly with SRP, and cargo unloading are inextricably linked to each other via conformational changes in FtsY. These allosteric communications allow the membrane delivery of cargo proteins to be efficiently coupled to their subsequent unloading and translocation, thus providing spatial coordination during protein targeting.

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 SecYEG activates GTPases to drive the completion of cotranslational protein targeting

2013 ◽  
Vol 200 (4) ◽  
pp. 397-405 ◽  
Author(s):  
David Akopian ◽  
Kush Dalal ◽  
Kuang Shen ◽  
Franck Duong ◽  
Shu-ou Shan
Keyword(s):  
Conformational Changes ◽  
Protein Targeting ◽  
Signal Recognition Particle ◽  
Signal Recognition ◽  
Conducting Channel ◽  
Gtp Hydrolysis ◽  
Efficient Delivery ◽  
Target Membrane

Signal recognition particle (SRP) and its receptor (SR) comprise a highly conserved cellular machine that cotranslationally targets proteins to a protein-conducting channel, the bacterial SecYEG or eukaryotic Sec61p complex, at the target membrane. Whether SecYEG is a passive recipient of the translating ribosome or actively regulates this targeting machinery remains unclear. Here we show that SecYEG drives conformational changes in the cargo-loaded SRP–SR targeting complex that activate it for GTP hydrolysis and for handover of the translating ribosome. These results provide the first evidence that SecYEG actively drives the efficient delivery and unloading of translating ribosomes at the target membrane.

scholarly journals Mechanisms of membrane protein biogenesis

2014 ◽  
Vol 70 (a1) ◽  
pp. C1161-C1161
Author(s):  
Irmgard Sinning
Keyword(s):  
Membrane Proteins ◽  
Signal Sequence ◽  
Signal Recognition Particle ◽  
Signal Recognition ◽  
Protein Biogenesis ◽  
Cargo Proteins ◽  
Target Membrane ◽  
Hydrophobic Nature ◽  
Correct Target ◽  
Srp Rna

More than 25% of the cellular proteome comprise membrane proteins that have to be inserted into the correct target membrane. Most membrane proteins are delivered to the membrane by the signal recognition particle (SRP) pathway which relies on the recognition of an N-terminal signal sequence. In contrast to this co-translational mechanism, which avoids problems due to the hydrophobic nature of the cargo proteins, tail-anchored (TA) membrane proteins utilize a post-translational mechanism for membrane insertion – the GET pathway (guided entry of tail-anchored membrane proteins). The SRP and GET pathways are both regulated by GTP and ATP binding proteins of the SIMIBI family. However, in the SRP pathway the SRP RNA plays a unique regulatory role. Recent insights into eukaryotic SRP will be discussed.

scholarly journals Fingerloop activates cargo delivery and unloading during cotranslational protein targeting

2013 ◽  
Vol 24 (2) ◽  
pp. 63-73 ◽  
Author(s):  
Aileen R. Ariosa ◽  
Stacy S. Duncan ◽  
Ishu Saraogi ◽  
Xiaodong Lu ◽  
April Brown ◽  
...  
Keyword(s):  
Protein Targeting ◽  
Signal Sequence ◽  
Signal Recognition Particle ◽  
Structural Element ◽  
Cargo Delivery ◽  
Structural Work ◽  
Cargo Proteins ◽  
Target Membrane ◽  
Binding Groove ◽  
Gtpase Activation

During cotranslational protein targeting by the signal recognition particle (SRP), information about signal sequence binding in the SRP's M domain must be effectively communicated to its GTPase domain to turn on its interaction with the SRP receptor (SR) and thus deliver the cargo proteins to the membrane. A universally conserved “fingerloop” lines the signal sequence–binding groove of SRP; the precise role of this fingerloop in protein targeting has remained elusive. In this study, we show that the fingerloop plays important roles in SRP function by helping to induce the SRP into a more active conformation that facilitates multiple steps in the pathway, including efficient recruitment of SR, GTPase activation in the SRP•SR complex, and most significantly, the unloading of cargo onto the target membrane. On the basis of these results and recent structural work, we propose that the fingerloop is the first structural element to detect signal sequence binding; this information is relayed to the linker connecting the SRP's M and G domains and thus activates the SRP and SR for carrying out downstream steps in the pathway.

scholarly journals Structure, dynamics and interactions of large SRP variants

2019 ◽  
Vol 401 (1) ◽  
pp. 63-80 ◽  
Author(s):  
Klemens Wild ◽  
Matthias M.M. Becker ◽  
Georg Kempf ◽  
Irmgard Sinning
Keyword(s):  
Protein Targeting ◽  
Signal Recognition Particle ◽  
Domain Architecture ◽  
Particle Dynamics ◽  
Signal Recognition ◽  
Chain Complexes ◽  
Nascent Chain ◽  
Target Membrane ◽  
Signal Anchor ◽  
Srp Rna

Abstract Co-translational protein targeting to membranes relies on the signal recognition particle (SRP) system consisting of a cytosolic ribonucleoprotein complex and its membrane-associated receptor. SRP recognizes N-terminal cleavable signals or signal anchor sequences, retards translation, and delivers ribosome-nascent chain complexes (RNCs) to vacant translocation channels in the target membrane. While our mechanistic understanding is well advanced for the small bacterial systems it lags behind for the large bacterial, archaeal and eukaryotic SRP variants including an Alu and an S domain. Here we describe recent advances on structural and functional insights in domain architecture, particle dynamics and interplay with RNCs and translocon and GTP-dependent regulation of co-translational protein targeting stimulated by SRP RNA.

scholarly journals Efficient Interaction between Two GTPases Allows the Chloroplast SRP Pathway to Bypass the Requirement for an SRP RNA

2007 ◽  
Vol 18 (7) ◽  
pp. 2636-2645 ◽  
Author(s):  
Peera Jaru-Ampornpan ◽  
Sowmya Chandrasekar ◽  
Shu-ou Shan
Keyword(s):  
Complex Formation ◽  
Conformational Changes ◽  
Protein Targeting ◽  
Signal Recognition Particle ◽  
The Other ◽  
Signal Recognition ◽  
Binding Partner ◽  
Biochemical Analyses ◽  
Kinetics Of ◽  
Srp Rna

Cotranslational protein targeting to membranes is regulated by two GTPases in the signal recognition particle (SRP) and the SRP receptor; association between the two GTPases is slow and is accelerated 400-fold by the SRP RNA. Intriguingly, the otherwise universally conserved SRP RNA is missing in a novel chloroplast SRP pathway. We found that even in the absence of an SRP RNA, the chloroplast SRP and receptor GTPases can interact efficiently with one another; the kinetics of interaction between the chloroplast GTPases is 400-fold faster than their bacterial homologues, and matches the rate at which the bacterial SRP and receptor interact with the help of SRP RNA. Biochemical analyses further suggest that the chloroplast SRP receptor is pre-organized in a conformation that allows optimal interaction with its binding partner, so that conformational changes during complex formation are minimized. Our results highlight intriguing differences between the classical and chloroplast SRP and SRP receptor GTPases, and help explain how the chloroplast SRP pathway can mediate efficient targeting of proteins to the thylakoid membrane in the absence of the SRP RNA, which plays an indispensable role in all the other SRP pathways.

scholarly journals The Signal Recognition Particle (SRP) RNA Links Conformational Changes in the SRP to Protein Targeting

2007 ◽  
Vol 18 (7) ◽  
pp. 2728-2734 ◽  
Author(s):  
Niels Bradshaw ◽  
Peter Walter
Keyword(s):  
Conformational Changes ◽  
Protein Targeting ◽  
Signal Sequence ◽  
Signal Recognition Particle ◽  
Signal Recognition ◽  
Gtp Hydrolysis ◽  
E Coli ◽  
Srp Rna ◽  
Binding Subunit

The RNA component of the signal recognition particle (SRP) is universally required for cotranslational protein targeting. Biochemical studies have shown that SRP RNA participates in the central step of protein targeting by catalyzing the interaction of the SRP with the SRP receptor (SR). SRP RNA also accelerates GTP hydrolysis in the SRP·SR complex once formed. Using a reverse-genetic and biochemical analysis, we identified mutations in the E. coli SRP protein, Ffh, that abrogate the activity of the SRP RNA and cause corresponding targeting defects in vivo. The mutations in Ffh that disrupt SRP RNA activity map to regions that undergo dramatic conformational changes during the targeting reaction, suggesting that the activity of the SRP RNA is linked to the major conformational changes in the signal sequence-binding subunit of the SRP. In this way, the SRP RNA may coordinate the interaction of the SRP and the SR with ribosome recruitment and transfer to the translocon, explaining why the SRP RNA is an indispensable component of the protein targeting machinery.

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.

Sign in / Sign up

Export Citation Format

Share Document