From bacteria to chloroplasts: evolution of the chloroplast SRP system

2017 ◽  
Vol 398 (5-6) ◽  
pp. 653-661 ◽  
Author(s):  
Dominik Ziehe ◽  
Beatrix Dünschede ◽  
Danja Schünemann
Keyword(s):  
Plasma Membrane ◽  
Thylakoid Membrane ◽  
Protein Transport ◽  
Higher Plants ◽  
Signal Recognition Particle ◽  
Great Majority ◽  
Signal Recognition ◽  
Transport Mechanisms ◽  
Thylakoid Membrane Proteins ◽  
Lower Plants

Abstract Chloroplasts derive from a prokaryotic symbiont that lost most of its genes during evolution. As a result, the great majority of chloroplast proteins are encoded in the nucleus and are posttranslationally imported into the organelle. The chloroplast genome encodes only a few proteins. These include several multispan thylakoid membrane proteins which are synthesized on thylakoid-bound ribosomes and cotranslationally inserted into the membrane. During evolution, ancient prokaryotic targeting machineries were adapted and combined with novel targeting mechanisms to facilitate post- and cotranslational protein transport in chloroplasts. This review focusses on the chloroplast signal recognition particle (cpSRP) protein transport system, which has been intensively studied in higher plants. The cpSRP system derived from the prokaryotic SRP pathway, which mediates the cotranslational protein transport to the bacterial plasma membrane. Chloroplasts contain homologs of several components of the bacterial SRP system. The function of these conserved components in post- and/or cotranslational protein transport and chloroplast-specific modifications of these transport mechanisms are described. Furthermore, recent studies of cpSRP systems in algae and lower plants are summarized and their impact on understanding the evolution of the cpSRP system are discussed.

The complexity of pathways for protein import into thylakoids: it's not easy being green

2005 ◽  
Vol 33 (5) ◽  
pp. 1024-1027 ◽  
Author(s):  
A. Di Cola ◽  
E. Klostermann ◽  
C. Robinson
Keyword(s):  
Membrane Proteins ◽  
Thylakoid Membrane ◽  
Protein Import ◽  
Signal Recognition Particle ◽  
Integral Membrane Proteins ◽  
The Other ◽  
Signal Recognition ◽  
Transport Mechanisms ◽  
Insertion Mechanism

Numerous proteins are transported into or across the chloroplast thylakoid membrane. To date, two major pathways have been identified for the transport of luminal proteins (the Sec- and Tat-dependent pathways) and it is now clear that these protein translocases use fundamentally different transport mechanisms. Integral membrane proteins are inserted by means of at least two further pathways. One involves the input of numerous targeting factors, including SRP (signal recognition particle), FtsY and Albino3. Surprisingly, the other pathway does not involve any of the known chloroplastic targeting factors, and insertion is energy-independent, raising the possibility of an unusual ‘spontaneous’ insertion mechanism.

scholarly journals Binding of chloroplast signal recognition particle to a thylakoid membrane protein substrate in aqueous solution and delineation of the cpSRP43–substrate interaction domain

2011 ◽  
Vol 437 (1) ◽  
pp. 149-155 ◽  
Author(s):  
Peter Cain ◽  
Iris Holdermann ◽  
Irmgard Sinning ◽  
Arthur E. Johnson ◽  
Colin Robinson
Keyword(s):  
Aqueous Solution ◽  
Membrane Protein ◽  
Thylakoid Membrane ◽  
Mode Of Action ◽  
Signal Recognition Particle ◽  
Cross Linking ◽  
Signal Recognition ◽  
Cross Link ◽  
Protein Substrate ◽  
Substrate Interaction

A cpSRP [chloroplast SRP (signal recognition particle)] comprising cpSRP54 and cpSRP43 subunits mediates the insertion of light-harvesting proteins into the thylakoid membrane. We dissected its interaction with a full-length membrane protein substrate in aqueous solution by insertion of site-specific photo-activatable cross-linkers into in vitro-synthesized Lhcb1 (major light-harvesting chlorophyll-binding protein of photosystem II). We show that Lhcb1 residues 166–176 cross-link specifically to the cpSRP43 subunit. Some cross-link positions within Lhcb1 are in the ‘L18’ peptide required for targeting of cpSRP substrates, whereas other cross-linking positions define a new targeting signal in the third transmembrane span. Lhcb1 was not found to cross-link to cpSRP54 at any position, and cross-linking to cpSRP43 is unaffected by the absence of cpSRP54. cpSRP43 thus effectively binds substrates autonomously, and its ability to independently bind an extended 20+-residue substrate region highlights a major difference with other SRP types where the SRP54 subunit binds to hydrophobic target sequences. The results also show that cpSRP43 can bind to a hydrophobic, three-membrane span, substrate in aqueous solution, presumably reflecting a role for cpSRP in the chloroplast stroma. This mode of action, and the specificity of the cpSRP43–substrate interaction, may be associated with cpSRP's unique post-translational mode of action.

scholarly journals In Vitro Studies with Purified Components Reveal Signal Recognition Particle (SRP) and SecA/SecB as Constituents of Two Independent Protein-targeting Pathways of Escherichia coli

1999 ◽  
Vol 10 (7) ◽  
pp. 2163-2173 ◽  
Author(s):  
Hans-Georg Koch ◽  
Thomas Hengelage ◽  
Christoph Neumann-Haefelin ◽  
Juan MacFarlane ◽  
Hedda K. Hoffschulte ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Plasma Membrane ◽  
Membrane Proteins ◽  
Signal Recognition Particle ◽  
Membrane Vesicles ◽  
Secretory Proteins ◽  
Signal Recognition ◽  
Free System ◽  
E Coli

The molecular requirements for the translocation of secretory proteins across, and the integration of membrane proteins into, the plasma membrane of Escherichia coli were compared. This was achieved in a novel cell-free system from E. coliwhich, by extensive subfractionation, was simultaneously rendered deficient in SecA/SecB and the signal recognition particle (SRP) components, Ffh (P48), 4.5S RNA, and FtsY. The integration of two membrane proteins into inside-out plasma membrane vesicles of E. coli required all three SRP components and could not be driven by SecA, SecB, and ΔμH+. In contrast, these were the only components required for the translocation of secretory proteins into membrane vesicles, a process in which the SRP components were completely inactive. Our results, while confirming previous in vivo studies, provide the first in vitro evidence for the dependence of the integration of polytopic inner membrane proteins on SRP in E. coli. Furthermore, they suggest that SRP and SecA/SecB have different substrate specificities resulting in two separate targeting mechanisms for membrane and secretory proteins in E. coli. Both targeting pathways intersect at the translocation pore because they are equally affected by a blocked translocation channel.

scholarly journals Promiscuous targeting of polytopic membrane proteins to SecYEG or YidC by the Escherichia coli signal recognition particle

2012 ◽  
Vol 23 (3) ◽  
pp. 464-479 ◽  
Author(s):  
Thomas Welte ◽  
Renuka Kudva ◽  
Patrick Kuhn ◽  
Lukas Sturm ◽  
David Braig ◽  
...  
Keyword(s):  
Membrane Proteins ◽  
Ribosomal Proteins ◽  
Protein Transport ◽  
Integration Site ◽  
Signal Recognition Particle ◽  
Cross Linking ◽  
Secretory Proteins ◽  
Signal Recognition ◽  
Protein Insertion ◽  
C Terminus

Protein insertion into the bacterial inner membrane is facilitated by SecYEG or YidC. Although SecYEG most likely constitutes the major integration site, small membrane proteins have been shown to integrate via YidC. We show that YidC can also integrate multispanning membrane proteins such as mannitol permease or TatC, which had been considered to be exclusively integrated by SecYEG. Only SecA-dependent multispanning membrane proteins strictly require SecYEG for integration, which suggests that SecA can only interact with the SecYEG translocon, but not with the YidC insertase. Targeting of multispanning membrane proteins to YidC is mediated by signal recognition particle (SRP), and we show by site-directed cross-linking that the C-terminus of YidC is in contact with SRP, the SRP receptor, and ribosomal proteins. These findings indicate that SRP recognizes membrane proteins independent of the downstream integration site and that many membrane proteins can probably use either SecYEG or YidC for integration. Because protein synthesis is much slower than protein transport, the use of YidC as an additional integration site for multispanning membrane proteins may prevent a situation in which the majority of SecYEG complexes are occupied by translating ribosomes during cotranslational insertion, impeding the translocation of secretory proteins.

scholarly journals cpSRP43 is both highly flexible and stable: Structural insights using a combined experimental and computational approach

2022 ◽  
Author(s):  
Mitchell Benton ◽  
Mercede Furr ◽  
Vivek Govind Kumar ◽  
Feng Gao ◽  
Colin D Heyes ◽  
...  
Keyword(s):  
Thylakoid Membrane ◽  
Higher Plants ◽  
Signal Recognition Particle ◽  
Dynamic Structure ◽  
Md Simulations ◽  
The Novel ◽  
External Energy ◽  
Conformational Landscape ◽  
High Flexibility ◽  
Structural Insights

The novel multidomain protein, cpSRP43, is a unique subunit of the post-translational chloroplast signal recognition particle (cpSRP) targeting pathway in higher plants. The cpSRP pathway is responsible for targeting and insertion of light-harvesting chlorophyll a/b binding proteins (LHCPs) to the thylakoid membrane. Nuclear-encoded LHCPs are synthesized in the cytoplasm then imported into the chloroplast. Upon emergence into the stroma, LHCPs form a soluble transit complex with the cpSRP heterodimer, which is composed of cpSRP43 and cpSRP54, a 54 kDa subunit homologous to the universally conserved GTPase in cytosolic SRP pathways. cpSRP43 is irreplaceable as a chaperone to LHCPs in their translocation to the thylakoid membrane and remarkable in its ability to dissolve aggregates of LHCPs without the need for external energy input. In previous studies, cpSRP43 has demonstrated significant flexibility and interdomain dynamics. However, the high flexibility and structural dynamics of cpSRP43 is yet unexplained by current crystal structures of cpSRP43. This is due, in part, to the fact that free full length cpSRP43 is so flexible that it is unable to crystalize. In this study, we explore the structural stability of cpSRP43 under different conditions using various biophysical techniques and find that this protein is concurrently highly stable and flexible. This conclusion is interesting considering that stable proteins typically possess a non-dynamic structure. Molecular dynamics (MD) simulations which correlated with data from biophysical experimentation were used to explain the basis of the extraordinary stability of cpSRP43. This combination of biophysical data and microsecond-level MD simulations allows us to obtain a detailed perspective of the conformational landscape of these proteins.

Peptide nucleic acid mediated inhibition of the bacterial signal recognition particle

2018 ◽  
Vol 54 (59) ◽  
pp. 8257-8260 ◽  
Author(s):  
Sudipta Ghosh ◽  
Snehlata Saini ◽  
Ishu Saraogi
Keyword(s):  
Nucleic Acid ◽  
Peptide Nucleic Acid ◽  
Protein Transport ◽  
Signal Recognition Particle ◽  
Signal Recognition ◽  
Antibacterial Target ◽  
First Time

Here we propose and validate the signal recognition particle (SRP), a protein transport machinery, as an antibacterial target for the first time.

scholarly journals Molecular Mimicry of SecA and Signal Recognition Particle Binding to the Bacterial Ribosome

mBio ◽  
2019 ◽  
Vol 10 (4) ◽  
Author(s):  
Lara Knüpffer ◽  
Clara Fehrenbach ◽  
Kärt Denks ◽  
Veronika Erichsen ◽  
Narcis-Adrian Petriman ◽  
...  
Keyword(s):  
Protein Transport ◽  
Molecular Mimicry ◽  
Signal Recognition Particle ◽  
Transport Systems ◽  
Secretory Proteins ◽  
Signal Recognition ◽  
Bacterial Protein ◽  
Ribosomal Tunnel ◽  
N Terminus ◽  
Nascent Chain

ABSTRACT Bacteria execute a variety of protein transport systems for maintaining the proper composition of their different cellular compartments. The SecYEG translocon serves as primary transport channel and is engaged in transporting two different substrate types. Inner membrane proteins are cotranslationally inserted into the membrane after their targeting by the signal recognition particle (SRP). In contrast, secretory proteins are posttranslationally translocated by the ATPase SecA. Recent data indicate that SecA can also bind to ribosomes close to the tunnel exit. We have mapped the interaction of SecA with translating and nontranslating ribosomes and demonstrate that the N terminus and the helical linker domain of SecA bind to an acidic patch on the surface of the ribosomal protein uL23. Intriguingly, both also insert deeply into the ribosomal tunnel to contact the intratunnel loop of uL23, which serves as a nascent chain sensor. This binding pattern is remarkably similar to that of SRP and indicates an identical interaction mode of the two targeting factors with ribosomes. In the presence of a nascent chain, SecA retracts from the tunnel but maintains contact with the surface of uL23. Our data further demonstrate that ribosome and membrane binding of SecA are mutually exclusive, as both events depend on the N terminus of SecA. Our study highlights the enormous plasticity of bacterial protein transport systems and reveals that the discrimination between SRP and SecA substrates is already initiated at the ribosome. IMPORTANCE Bacterial protein transport via the conserved SecYEG translocon is generally classified as either cotranslational, i.e., when transport is coupled to translation, or posttranslational, when translation and transport are separated. We show here that the ATPase SecA, which is considered to bind its substrates posttranslationally, already scans the ribosomal tunnel for potential substrates. In the presence of a nascent chain, SecA retracts from the tunnel but maintains contact with the ribosomal surface. This is remarkably similar to the ribosome-binding mode of the signal recognition particle, which mediates cotranslational transport. Our data reveal a striking plasticity of protein transport pathways, which likely enable bacteria to efficiently recognize and transport a large number of highly different substrates within their short generation time.

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