A signal-anchor sequence stimulates signal recognition particle binding to ribosomes from inside the exit tunnel

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.

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Fluorescence-detected assembly of the signal recognition particle: binding of the two SRP protein heterodimers to SRP RNA is noncooperative

Biochemistry ◽

10.1021/bi00140a019 ◽

1992 ◽

Vol 31 (25) ◽

pp. 5830-5840 ◽

Cited By ~ 23

Author(s):

Fabiola Janiak ◽

Peter Walter ◽

Arthur E. Johnson

Keyword(s):

Signal Recognition Particle ◽

Signal Recognition ◽

Particle Binding ◽

Srp Rna

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Decision letter: Real-time observation of signal recognition particle binding to actively translating ribosomes

10.7554/elife.04418.017 ◽

2014 ◽

Keyword(s):

Real Time ◽

Signal Recognition Particle ◽

Signal Recognition ◽

Particle Binding ◽

Time Observation ◽

Real Time Observation

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Interplay of signal recognition particle and trigger factor at L23 near the nascent chain exit site on the Escherichia coli ribosome

The Journal of Cell Biology ◽

10.1083/jcb.200302130 ◽

2003 ◽

Vol 161 (4) ◽

pp. 679-684 ◽

Cited By ~ 93

Author(s):

Ronald S. Ullers ◽

Edith N.G. Houben ◽

Amanda Raine ◽

Corinne M. ten Hagen-Jongman ◽

Måns Ehrenberg ◽

...

Keyword(s):

Escherichia Coli ◽

Ribosomal Proteins ◽

Signal Recognition Particle ◽

Attachment Site ◽

Trigger Factor ◽

Signal Recognition ◽

Exit Site ◽

Nascent Chain ◽

Signal Anchor

As newly synthesized polypeptides emerge from the ribosome, they interact with chaperones and targeting factors that assist in folding and targeting to the proper location in the cell. In Escherichia coli, the chaperone trigger factor (TF) binds to nascent polypeptides early in biosynthesis facilitated by its affinity for the ribosomal proteins L23 and L29 that are situated around the nascent chain exit site on the ribosome. The targeting factor signal recognition particle (SRP) interacts specifically with the signal anchor (SA) sequence in nascent inner membrane proteins (IMPs). Here, we have used photocross-linking to map interactions of the SA sequence in a short, in vitro–synthesized, nascent IMP. Both TF and SRP were found to interact with the SA with partially overlapping binding specificity. In addition, extensive contacts with L23 and L29 were detected. Both purified TF and SRP could be cross-linked to L23 on nontranslating ribosomes with a competitive advantage for SRP. The results suggest a role for L23 in the targeting of IMPs as an attachment site for TF and SRP that is close to the emerging nascent chain.

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Archaea Signal Recognition Particle Shows the Way

Archaea ◽

10.1155/2010/485051 ◽

2010 ◽

Vol 2010 ◽

pp. 1-11 ◽

Cited By ~ 10

Author(s):

Christian Zwieb ◽

Shakhawat Bhuiyan

Keyword(s):

Signal Sequence ◽

Signal Recognition Particle ◽

Signal Recognition ◽

R Region ◽

Exit Tunnel ◽

And Function ◽

Hydrolysis Of ◽

Subordinate Role ◽

Srp Rna

Archaea SRP is composed of an SRP RNA molecule and two bound proteins named SRP19 and SRP54. Regulated by the binding and hydrolysis of guanosine triphosphates, the RNA-bound SRP54 protein transiently associates not only with the hydrophobic signal sequence as it emerges from the ribosomal exit tunnel, but also interacts with the membrane-associated SRP receptor (FtsY). Comparative analyses of the archaea genomes and their SRP component sequences, combined with structural and biochemical data, support a prominent role of the SRP RNA in the assembly and function of the archaea SRP. The 5e motif, which in eukaryotes binds a 72 kilodalton protein, is preserved in most archaea SRP RNAs despite the lack of an archaea SRP72 homolog. The primary function of the 5e region may be to serve as a hinge, strategically positioned between the small and large SRP domain, allowing the elongated SRP to bind simultaneously to distant ribosomal sites. SRP19, required in eukaryotes for initiating SRP assembly, appears to play a subordinate role in the archaea SRP or may be defunct. The N-terminal A region and a novel C-terminal R region of the archaea SRP receptor (FtsY) are strikingly diverse or absent even among the members of a taxonomic subgroup.

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Structures of the scanning and engaged states of the mammalian SRP-ribosome complex

eLife ◽

10.7554/elife.07975 ◽

2015 ◽

Vol 4 ◽

Cited By ~ 60

Author(s):

Rebecca M Voorhees ◽

Ramanujan S Hegde

Keyword(s):

Signal Recognition Particle ◽

Signal Recognition ◽

Amphipathic Helix ◽

Translation Elongation ◽

Chain Complexes ◽

Nascent Chain ◽

Hydrophobic Binding ◽

Targeting Signal ◽

Exit Tunnel ◽

Binding Groove

The universally conserved signal recognition particle (SRP) is essential for the biogenesis of most integral membrane proteins. SRP scans the nascent chains of translating ribosomes, preferentially engaging those with hydrophobic targeting signals, and delivers these ribosome-nascent chain complexes to the membrane. Here, we present structures of native mammalian SRP-ribosome complexes in the scanning and engaged states. These structures reveal the near-identical SRP architecture of these two states, show many of the SRP-ribosome interactions at atomic resolution, and suggest how the polypeptide-binding M domain selectively engages hydrophobic signals. The scanning M domain, pre-positioned at the ribosomal exit tunnel, is auto-inhibited by a C-terminal amphipathic helix occluding its hydrophobic binding groove. Upon engagement, the hydrophobic targeting signal displaces this amphipathic helix, which then acts as a protective lid over the signal. Biochemical experiments suggest how scanning and engagement are coordinated with translation elongation to minimize exposure of hydrophobic signals during membrane targeting.

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