scholarly journals GTP hydrolysis by complexes of the signal recognition particle and the signal recognition particle receptor.

1993 ◽  
Vol 123 (4) ◽  
pp. 799-807 ◽  
Author(s):  
T Connolly ◽  
R Gilmore
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Translocation ◽  
Signal Recognition Particle ◽  
Hydrolysis Rate ◽  
Endoplasmic Reticulum Membrane ◽  
Signal Recognition ◽  
Gtp Hydrolysis ◽  
Receptor Complexes ◽  
Gtp Binding ◽  
Hydrolysis Activity

Translocation of proteins across the endoplasmic reticulum membrane is a GTP-dependent process. The signal recognition particle (SRP) and the SRP receptor both contain subunits with GTP binding domains. One GTP-dependent reaction during protein translocation is the SRP receptor-mediated dissociation of SRP from the signal sequence of a nascent polypeptide. Here, we have assayed the SRP and the SRP receptor for GTP binding and hydrolysis activities. GTP hydrolysis by SRP was not detected, so the maximal GTP hydrolysis rate for SRP was estimated to be < 0.002 mol GTP hydrolyzed x mol of SRP-1 x min-1. The intrinsic GTP hydrolysis activity of the SRP receptor ranged between 0.02 and 0.04 mol GTP hydrolyzed x mol of SRP receptor-1 x min-1. A 40-fold enhancement of GTP hydrolysis activity relative to that observed for the SRP receptor alone was obtained when complexes were formed between SRP and the SRP receptor. GTP hydrolysis activity was inhibited by GDP, but not by ATP. Extended incubation of the SRP or the SRP receptor with GTP resulted in substoichiometric quantities of protein-bound ribonucleotide. SRP-SRP receptor complexes engaged in GTP hydrolysis were found to contain a minimum of one bound guanine ribonucleotide per SRP-SRP receptor complex. We conclude that the GTP hydrolysis activity described here is indicative of one of the GTPase cycles that occur during protein translocation across the endoplasmic reticulum.

scholarly journals Direct probing of the interaction between the signal sequence of nascent preprolactin and the signal recognition particle by specific cross-linking.

1987 ◽  
Vol 104 (2) ◽  
pp. 201-208 ◽  
Author(s):  
M Wiedmann ◽  
T V Kurzchalia ◽  
H Bielka ◽  
T A Rapoport
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Translocation ◽  
Signal Sequence ◽  
Signal Recognition Particle ◽  
Cross Linking ◽  
Endoplasmic Reticulum Membrane ◽  
Signal Recognition ◽  
Group 4 ◽  
Lysine Residues ◽  
Nascent Chain

We have studied the interaction between the signal sequence of nascent preprolactin and the signal recognition particle (SRP) during the initial events in protein translocation across the endoplasmic reticulum membrane. A new method of affinity labeling was used, whereby lysine residues, carrying the photoreactive group 4-(3-trifluoromethyldiazirino) benzoic acid in their side chains, are incorporated into a protein by means of modified lysyl-tRNA, and cross-linking to the interacting component is induced by irradiation. SRP interacts through its Mr 54,000 polypeptide component with the signal sequences of nascent preprolactin chains containing about 70 residues, and with decreasing affinity with longer chains as well; it causes inhibition of elongation. Binding of SRP is reversible and requires the nascent chain to be bound to a functional ribosome. SRP cross-linked to the signal sequence still inhibits elongation but does not prevent it completely. We conclude that SRP does not block the exit site of the polypeptide chain on the ribosome. The SRP receptor of the endoplasmic reticulum membrane displaces the signal sequence from SRP and, even if SRP is cross-linked, releases elongation arrest.

scholarly journals GTP-binding proteins may stimulate insulin biosynthesis in rat pancreatic islets by enhancing the signal-recognition-particle-dependent translocation of the insulin mRNA poly-/mono-some complex to the endoplasmic reticulum

1991 ◽  
Vol 275 (1) ◽  
pp. 23-28 ◽  
Author(s):  
N Welsh ◽  
C Oberg ◽  
M Welsh
Keyword(s):  
Endoplasmic Reticulum ◽  
Binding Proteins ◽  
Specific Binding ◽  
Signal Recognition Particle ◽  
Insulin Biosynthesis ◽  
Signal Recognition ◽  
Insulin Synthesis ◽  
Gtp Binding Proteins ◽  
Gtp Binding ◽  
Insulin Mrna

We aimed to elucidate the putative role of GTP-binding proteins in the regulation of insulin biosynthesis. For this purpose, freshly isolated rat islets were incubated in the presence of liposomes containing GDP, guanosine 5′-[beta-thio]diphosphate (GDP[S]), GTP, guanosine 5′-[gamma-thio]triphosphate (GTP[S]), guanosine 5′-[beta gamma-methylene]triphosphate (p[CH2]ppG), guanosine 5′[beta gamma-imido]triphosphate (p[NH]ppG) and ATP, and the effects of the liposomal delivery of these substances on rates of biosynthesis of insulin and total protein were determined. Insulin biosynthesis during a 1 h incubation at 1.67 mM-glucose was stimulated by ATP- and GTP[S]-containing liposomes as compared with control liposomes. At 16.7 mM-glucose, only the GTP[S]-containing liposomes stimulated insulin biosynthesis. No inhibition of islet protein and insulin synthesis was observed with GDP-, GDP[S]-, p[CH2]ppG- and p[NH]ppG-containing liposomes. By determining the subcellular distribution of insulin mRNA, it was found that the mRNA content associated with microsomes was increased and that associated with the cytosolic mono-/poly-somes decreased when the islets were incubated with GTP[S]-containing liposomes, resulting in an approximate doubling of the ratio of microsomal to polysomal-associated insulin mRNA. ATP-containing liposomes produced no effects on the association of insulin mRNA with microsomes. By using photoaffinity labelling and immunoprecipitation techniques, specific binding of GTP[35S] to the alpha-subunit of the signal-recognition particle (SRP) receptor in islet homogenates containing physiological concentrations of GTP and GDP was demonstrated. These findings suggest that the GTP-binding subunit(s) of the SRP receptor, and possibly also of other GTP-binding proteins involved in this process, may regulate insulin biosynthesis by stimulating the translocation of insulin mRNA to the endoplasmic reticulum and by increasing preproinsulin-peptide translocation into the lumen of the reticulum.

scholarly journals Subcellular distribution of signal recognition particle and 7SL-RNA determined with polypeptide-specific antibodies and complementary DNA probe.

1983 ◽  
Vol 97 (6) ◽  
pp. 1693-1699 ◽  
Author(s):  
P Walter ◽  
G Blobel
Keyword(s):  
Protein Translocation ◽  
Solid Phase ◽  
Signal Recognition Particle ◽  
Endoplasmic Reticulum Membrane ◽  
Signal Recognition ◽  
Specific Antibodies ◽  
7Sl Rna ◽  
Radioimmune Assay ◽  
Cell Fractions

Signal recognition particle (SRP) is a ribonucleoprotein consisting of six distinct polypeptides and one molecule of small cytoplasmic 7SL-RNA. The particle was previously shown to function in protein translocation across and protein integration into the endoplasmic reticulum membrane. Polypeptide specific antibodies were raised in rabbits against the 72,000-, 68,000-, and 54,000-mol-wt polypeptide of SRP. All three antibodies are shown to neutralize SRP activity in vitro. A solid phase radioimmune assay is described and used to follow SRP in various cell fractions. The partitioning of SRP is shown to be dependent on the ionic conditions of the fractionation. Under conditions approximating physiological ionic strength, SRP is found to be about equally distributed between a membrane associated (38%) and a free (15%) or ribosome associated (47%) state. Furthermore, it is shown that greater than 75% of the total cellular 7SL-RNA is associated with SRP polypeptide in these fractions. Thus it is likely that the major--if not the only--cellular function of 7SL-RNA is as a part of SRP.

Topology of signal recognition particle receptor in endoplasmic reticulum membrane

Nature ◽  
1985 ◽  
Vol 318 (6044) ◽  
pp. 334-338 ◽  
Author(s):  
Leander Lauffer ◽  
Pablo D. Garcia ◽  
Richard N. Harkins ◽  
Lisa Coussens ◽  
Axel Ullrich ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Signal Recognition Particle ◽  
Endoplasmic Reticulum Membrane ◽  
Signal Recognition ◽  
Signal Recognition Particle Receptor

scholarly journals Signal sequence recognition and targeting of ribosomes to the endoplasmic reticulum by the signal recognition particle do not require GTP.

1994 ◽  
Vol 5 (8) ◽  
pp. 887-897 ◽  
Author(s):  
P J Rapiejko ◽  
R Gilmore
Keyword(s):  
Protein Translocation ◽  
Signal Sequence ◽  
Signal Recognition Particle ◽  
Beta Subunits ◽  
Signal Recognition ◽  
Binding Assays ◽  
Nascent Polypeptide ◽  
Sequence Recognition ◽  
Gtp Binding ◽  
Microsomal Membranes

The identification of GTP-binding sites in the 54-kDa subunit of the signal recognition particle (SRP) and in both the alpha and beta subunits of the SRP receptor has complicated the task of defining the step in the protein translocation reaction that is controlled by the GTP-binding site in the SRP. Ribonucleotide binding assays show that the purified SRP can bind GDP or GTP. However, crosslinking experiments show that SRP54 can recognize the signal sequence of a nascent polypeptide in the absence of GTP. Targeting of SRP-ribosome-nascent polypeptide complexes, formed in the absence of GTP, to microsomal membranes likewise proceeds normally. To separate the GTPase cycles of SRP54 and the alpha subunit of the SRP receptor (SR alpha), we employed an SR alpha mutant that displays a markedly reduced affinity for GTP. We observed that the dissociation of SRP54 from the signal sequence and the insertion of the nascent polypeptide into the translocation site could only occur when GTP binding to SR alpha was permitted. These data suggest that the GTP binding and hydrolysis cycles of both SRP54 and SR alpha are initiated upon formation of the SRP-SRP receptor complex.

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.

Sign in / Sign up

Export Citation Format

Share Document