scholarly journals Identification of cytoplasmic residues of Sec61p involved in ribosome binding and cotranslational translocation

2005 ◽  
Vol 168 (1) ◽  
pp. 67-77 ◽  
Author(s):  
Zhiliang Cheng ◽  
Ying Jiang ◽  
Elisabet C. Mandon ◽  
Reid Gilmore
Keyword(s):  
Signal Recognition Particle ◽  
Point Mutations ◽  
Ribosomal Subunit ◽  
Chain Complex ◽  
Binding Activity ◽  
Initial Contact ◽  
Ribosome Binding ◽  
Cotranslational Translocation ◽  
Translocation Pathway ◽  
Cytoplasmic Loops

The cytoplasmic surface of Sec61p is the binding site for the ribosome and has been proposed to interact with the signal recognition particle receptor during targeting of the ribosome nascent chain complex to the translocation channel. Point mutations in cytoplasmic loops six (L6) and eight (L8) of yeast Sec61p cause reductions in growth rates and defects in the translocation of nascent polypeptides that use the cotranslational translocation pathway. Sec61 heterotrimers isolated from the L8 sec61 mutants have a greatly reduced affinity for 80S ribosomes. Cytoplasmic accumulation of protein precursors demonstrates that the initial contact between the large ribosomal subunit and the Sec61 complex is important for efficient insertion of a nascent polypeptide into the translocation pore. In contrast, point mutations in L6 of Sec61p inhibit cotranslational translocation without significantly reducing the ribosome-binding activity, indicating that the L6 and L8 sec61 mutants affect different steps in the cotranslational translocation pathway.

scholarly journals Ribosome binding to the endoplasmic reticulum: a 180-kD protein identified by crosslinking to membrane-bound ribosomes is not required for ribosome binding activity.

1991 ◽  
Vol 114 (4) ◽  
pp. 639-649 ◽  
Author(s):  
P G Collins ◽  
R Gilmore
Keyword(s):  
Signal Sequence ◽  
Signal Recognition Particle ◽  
Membrane Vesicles ◽  
Immunoblot Analysis ◽  
Binding Activity ◽  
Size Exclusion ◽  
Ribosome Binding ◽  
Specific Subset ◽  
Microsomal Membranes ◽  
Membrane Bound

We have used the membrane-impermeable, thiol-cleavable, crosslinker 3,3'-dithio bis (sulfosuccinimidylpropionate) to identify proteins that are in the vicinity of membrane-bound ribosomes of the RER. A specific subset of RER proteins was reproducibly crosslinked to the ribosome. Immunoblot analysis of the crosslinked products with antibodies raised against signal recognition particle receptor, ribophorin I, and the 35-kD subunit of the signal sequence receptor demonstrated that these translocation components had been crosslinked to the ribosome, but each to a different extent. The most prominent polypeptide among the crosslinked products was a 180-kD protein that has recently been proposed to be a ribosome receptor (Savitz, A.J., and D.I. Meyer, 1990. Nature (Lond.). 346: 540-544). RER membrane proteins were reconstituted into liposomes and assayed with radiolabeled ribosomes to determine whether ribosome binding activity could be ascribed to the 180-kD protein. Differential detergent extraction was used to prepare soluble extracts of microsomal membrane vesicles that either contained or lacked the 180-kD protein. Liposomes reconstituted from both extracts bound ribosomes with essentially identical affinity. Additional fractionation experiments demonstrated that the bulk of the ribosome binding activity present in detergent extracts of microsomal membranes could be readily resolved from the 180-kD protein by size exclusion chromatography. Taken together, we conclude that the 180-kD protein is in the vicinity of membrane bound ribosomes, yet does not correspond to the ribosome receptor.

scholarly journals Access to Ribosomal Protein Rpl25p by the Signal Recognition Particle Is Required for Efficient Cotranslational Translocation

2008 ◽  
Vol 19 (7) ◽  
pp. 2876-2884 ◽  
Author(s):  
Jane A. Dalley ◽  
Alexander Selkirk ◽  
Martin R. Pool
Keyword(s):  
Ribosomal Protein ◽  
Critical Role ◽  
Signal Recognition Particle ◽  
Signal Recognition ◽  
Structural Studies ◽  
Interaction Site ◽  
Ribosome Binding ◽  
Cotranslational Translocation ◽  
Dominant Mutant

Targeting of proteins to the endoplasmic reticulum (ER) occurs cotranslationally necessitating the interaction of the signal recognition particle (SRP) and the translocon with the ribosome. Biochemical and structural studies implicate ribosomal protein Rpl25p as a major ribosome interaction site for both these factors. Here we characterize an RPL25GFP fusion, which behaves as a dominant mutant leading to defects in co- but not posttranslational translocation in vivo. In these cells, ribosomes still interact with ER membrane and the translocon, but are defective in binding SRP. Overexpression of SRP can restore ribosome binding of SRP, but only partially rescues growth and translocation defects. Our results indicate that Rpl25p plays a critical role in the recruitment of SRP to the ribosome.

scholarly journals The signal sequence receptor, unlike the signal recognition particle receptor, is not essential for protein translocation

1992 ◽  
Vol 117 (1) ◽  
pp. 15-25 ◽  
Author(s):  
G Migliaccio ◽  
CV Nicchitta ◽  
G Blobel
Keyword(s):  
Membrane Protein ◽  
Protein Translocation ◽  
Signal Sequence ◽  
Signal Recognition Particle ◽  
Chain Complex ◽  
Secretory Protein ◽  
Signal Recognition ◽  
Ribosome Binding ◽  
Signal Recognition Particle Receptor ◽  
Nascent Chain

Detergent extracts of canine pancreas rough microsomal membranes were depleted of either the signal recognition particle receptor (SR), which mediates the signal recognition particle (SRP)-dependent targeting of the ribosome/nascent chain complex to the membrane, or the signal sequence receptor (SSR), which has been proposed to function as a membrane bound receptor for the newly targeted nascent chain and/or as a component of a multi-protein translocation complex responsible for transfer of the nascent chain across the membrane. Depletion of the two components was performed by chromatography of detergent extracts on immunoaffinity supports. Detergent extracts lacking either SR or SSR were reconstituted and assayed for activity with respect to SR dependent elongation arrest release, nascent chain targeting, ribosome binding, secretory precursor translocation, and membrane protein integration. Depletion of SR resulted in the loss of elongation arrest release activity, nascent chain targeting, secretory protein translocation, and membrane protein integration, although ribosome binding was unaffected. Full activity was restored by addition of immunoaffinity purified SR before reconstitution of the detergent extract. Surprisingly, depletion of SSR was without effect on any of the assayed activities, indicating that SSR is either not required for translocation or is one of a family of functionally redundant components.

scholarly journals An interaction between the SRP receptor and the translocon is critical during cotranslational protein translocation

2008 ◽  
Vol 180 (6) ◽  
pp. 1149-1161 ◽  
Author(s):  
Ying Jiang ◽  
Zhiliang Cheng ◽  
Elisabet C. Mandon ◽  
Reid Gilmore
Keyword(s):  
Protein Translocation ◽  
Signal Recognition Particle ◽  
Chain Complex ◽  
Growth Defect ◽  
Critical Function ◽  
Channel Interaction ◽  
Cotranslational Translocation ◽  
Efficient Delivery ◽  
Nascent Chain

The signal recognition particle (SRP)–dependent targeting pathway facilitates rapid, efficient delivery of the ribosome–nascent chain complex (RNC) to the protein translocation channel. We test whether the SRP receptor (SR) locates a vacant protein translocation channel by interacting with the yeast Sec61 and Ssh1 translocons. Surprisingly, the slow growth and cotranslational translocation defects caused by deletion of the transmembrane (TM) span of yeast SRβ (SRβ-ΔTM) are exaggerated when the SSH1 gene is disrupted. Disruption of the SBH2 gene, which encodes the β subunit of the Ssh1p complex, likewise causes a growth defect when combined with SRβ-ΔTM. Cotranslational translocation defects in the ssh1ΔSRβ-ΔTM mutant are explained by slow and inefficient in vivo gating of translocons by RNCs. A critical function for translocation channel β subunits in the SR–channel interaction is supported by the observation that simultaneous deletion of Sbh1p and Sbh2p causes a defect in the cotranslational targeting pathway that is similar to the translocation defect caused by deletion of either subunit of the SR.

scholarly journals Early encounters of a nascent membrane protein

2005 ◽  
Vol 170 (1) ◽  
pp. 27-35 ◽  
Author(s):  
Edith N.G. Houben ◽  
Raz Zarivach ◽  
Bauke Oudega ◽  
Joen Luirink
Keyword(s):  
Membrane Protein ◽  
Ribosomal Proteins ◽  
Transmembrane Domain ◽  
Signal Recognition Particle ◽  
Chain Complex ◽  
Signal Recognition ◽  
Inner Membrane ◽  
Ribosomal Tunnel ◽  
Nascent Chain ◽  
Inner Membrane Protein

An unbiased photo–cross-linking approach was used to probe the “molecular path” of a growing nascent Escherichia coli inner membrane protein (IMP) from the peptidyl transferase center to the surface of the ribosome. The nascent chain was initially in proximity to the ribosomal proteins L4 and L22 and subsequently contacted L23, which is indicative of progression through the ribosome via the main ribosomal tunnel. The signal recognition particle (SRP) started to interact with the nascent IMP and to target the ribosome–nascent chain complex to the Sec–YidC complex in the inner membrane when maximally half of the transmembrane domain (TM) was exposed from the ribosomal exit. The combined data suggest a flexible tunnel that may accommodate partially folded nascent proteins and parts of the SRP and SecY. Intraribosomal contacts of the nascent chain were not influenced by the presence of a functional TM in the ribosome.

scholarly journals Cotranslational Intersection between the SRP and GET Targeting Pathways to the Endoplasmic Reticulum of Saccharomyces cerevisiae

2016 ◽  
Vol 36 (18) ◽  
pp. 2374-2383 ◽  
Author(s):  
Ying Zhang ◽  
Thea Schäffer ◽  
Tina Wölfle ◽  
Edith Fitzke ◽  
Gerhard Thiel ◽  
...  
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Endoplasmic Reticulum ◽  
Transmembrane Domain ◽  
Signal Recognition Particle ◽  
Transmembrane Proteins ◽  
Signal Recognition ◽  
Ribosome Binding ◽  
Channel Proteins ◽  
Membrane Spanning ◽  
Combined Data

Targeting of transmembrane proteins to the endoplasmic reticulum (ER) proceeds via either the signal recognition particle (SRP) or the guided entry of tail-anchored proteins (GET) pathway, consisting of Get1 to -5 and Sgt2. While SRP cotranslationally targets membrane proteins containing one or multiple transmembrane domains, the GET pathway posttranslationally targets proteins containing a single C-terminal transmembrane domain termed the tail anchor. Here, we dissect the roles of the SRP and GET pathways in the sorting of homologous, two-membrane-spanning K+channel proteins termed Kcv, Kesv, and Kesv-VV. We show that Kcv is targeted to the ER cotranslationally via its N-terminal transmembrane domain, while Kesv-VV is targeted posttranslationally via its C-terminal transmembrane domain, which recruits Get4-5/Sgt2 and Get3. Unexpectedly, nascent Kcv recruited not only SRP but also the Get4-5 module of the GET pathway to ribosomes. Ribosome binding of Get4-5 was independent of Sgt2 and was strongly outcompeted by SRP. The combined data indicate a previously unrecognized cotranslational interplay between the SRP and GET pathways.

scholarly journals Interaction of nuclear proteins with a positive cis-acting element of rat embryonic myosin heavy-chain promoter: identification of a new transcriptional factor.

1989 ◽  
Vol 9 (5) ◽  
pp. 1839-1849 ◽  
Author(s):  
Y T Yu ◽  
B Nadal-Ginard
Keyword(s):  
Binding Site ◽  
Myosin Heavy Chain ◽  
Heavy Chain ◽  
Hela Cells ◽  
Promoter Activity ◽  
Point Mutations ◽  
Binding Activity ◽  
Transcriptional Factor ◽  
Binding Assays ◽  
Cis Acting

A DNA fragment of the rat embryonic myosin heavy-chain promoter (MHCemb) has been found to specifically bind a nuclear factor (NFe) present in extracts prepared from mouse C2 myoblasts, myotubes, and HeLa cells. The nucleotide sequence of the binding site (BSe) has been identified as 5'-GTGTCAGTCA-3' and was located between -93 and -84. Transient expression studies on MHCemb promoter deletion constructs in C2 myoblasts and C2 myotubes suggested that NFe is a transcriptional factor. Deletion of the NFe-binding site resulted in four- to sixfold and twofold reduction of promoter activity in C2 myotubes and C2 myoblasts, respectively. Furthermore, point mutations at the BSe not only abolished the NFe-binding activity of the MHCemb promoter but also resulted in reduction of the promoter activity to levels similar to those of the deletion constructs in C2 myotubes, myoblasts, and Hela cells (four- to sixfold). Although BSe and the binding site of the recently identified transcriptional factors AP-1 and ATF share significant homology, the results from competition binding assays indicated that NFe is different from both AP-1 and ATF.

scholarly journals Ribosome binding induces repositioning of the signal recognition particle receptor on the translocon

2015 ◽  
Vol 211 (1) ◽  
pp. 91-104 ◽  
Author(s):  
Patrick Kuhn ◽  
Albena Draycheva ◽  
Andreas Vogt ◽  
Narcis-Adrian Petriman ◽  
Lukas Sturm ◽  
...  
Keyword(s):  
Protein Targeting ◽  
Signal Recognition Particle ◽  
Resonance Energy Transfer ◽  
Chain Complex ◽  
Resonance Energy ◽  
Endoplasmic Reticulum Membrane ◽  
Signal Recognition ◽  
Ribosomal Tunnel ◽  
Nascent Chain

Cotranslational protein targeting delivers proteins to the bacterial cytoplasmic membrane or to the eukaryotic endoplasmic reticulum membrane. The signal recognition particle (SRP) binds to signal sequences emerging from the ribosomal tunnel and targets the ribosome-nascent-chain complex (RNC) to the SRP receptor, termed FtsY in bacteria. FtsY interacts with the fifth cytosolic loop of SecY in the SecYEG translocon, but the functional role of the interaction is unclear. By using photo-cross-linking and fluorescence resonance energy transfer measurements, we show that FtsY–SecY complex formation is guanosine triphosphate independent but requires a phospholipid environment. Binding of an SRP–RNC complex exposing a hydrophobic transmembrane segment induces a rearrangement of the SecY–FtsY complex, which allows the subsequent contact between SecY and ribosomal protein uL23. These results suggest that direct RNC transfer to the translocon is guided by the interaction between SRP and translocon-bound FtsY in a quaternary targeting complex.

scholarly journals Dynamic Interactions between Pit-1 and C/EBPα in the Pituitary Cell Nucleus

2006 ◽  
Vol 26 (21) ◽  
pp. 8087-8098 ◽  
Author(s):  
Ignacio A. Demarco ◽  
Ty C. Voss ◽  
Cynthia F. Booker ◽  
Richard N. Day
Keyword(s):  
Transcriptional Control ◽  
Point Mutations ◽  
Binding Activity ◽  
Hormone Deficiency ◽  
Pituitary Hormone ◽  
Pituitary Cells ◽  
Dynamic Interactions ◽  
Dna Binding Activity ◽  
Control Patterns ◽  
Α Helix

ABSTRACT The homeodomain (HD) transcription factors are a structurally conserved family of proteins that, through networks of interactions with other nuclear proteins, control patterns of gene expression during development. For example, the network interactions of the pituitary-specific HD protein Pit-1 control the development of anterior pituitary cells and regulate the expression of the hormone products in the adult cells. Inactivating mutations in Pit-1 disrupt these processes, giving rise to the syndrome of combined pituitary hormone deficiency. Pit-1 interacts with CCAAT/enhancer-binding protein alpha (C/EBPα) to regulate prolactin transcription. Here, we used the combination of biochemical analysis and live-cell microscopy to show that two different point mutations in Pit-1, which disrupted distinct activities, affected the dynamic interactions between Pit-1 and C/EBPα in different ways. The results showed that the first α-helix of the POU-S domain is critical for the assembly of Pit-1 with C/EBPα, and they showed that DNA-binding activity conferred by the HD is critical for the final intranuclear positioning of the metastable complex. This likely reflects more general mechanisms that govern cell-type-specific transcriptional control, and the results from the analysis of the point mutations could indicate an important link between the mislocalization of transcriptional complexes and disease processes.

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