SRbeta coordinates signal sequence release from SRP with ribosome binding to the translocon.
Protein targeting to the endoplasmic reticulum (ER) membrane is regulated by three GTPases, the 54 kDa subunit of the signal recognition particle (SRP) and the alpha- and beta-subunits of the SRP receptor (SR). Using a soluble form of SR and an XTP-binding mutant of SRbeta, we show that SRbeta is essential for protein translocation across the ER membrane. SRbeta can be cross-linked to a 21 kDa ribosomal protein in its empty and GDP-bound state, but not when GTP is bound. GTP binding to SRbeta is required to induce signal sequence release from SRP. This is achieved by the presence of the translocon, which changes the interaction between the 21 kDa ribosomal protein and SRbeta and thereby allows SRbeta to bind GTP. We conclude that SRbeta coordinates the release of the signal sequence from SRP with the presence of the translocon.
Fulga
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Structural Biology Programme, European Molecular Biology Laboratory (EMBL), D-69117 Heidelberg, Germany.
Sinning
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Dobberstein
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Pool
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D000818:Animals; D002474:Cell-Free System; D004285:Dogs; D020558:GTP Phosphohydrolases / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding / Q000502:physiology; D021382:Protein Sorting Signals / Q000502:physiology*; D017434:Protein Structure, Tertiary / Q000502:physiology; D021122:Protein Subunits; D021381:Protein Transport / Q000502:physiology; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism*; D018000:Receptors, Peptide / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012269:Ribosomal Proteins / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism*; D000069816:SEC Translocation Channels; D018271:Signal Recognition Particle / Q000378:metabolism*
D008565:Membrane Proteins; D021382:Protein Sorting Signals; D021122:Protein Subunits; D018160:Receptors, Cytoplasmic and Nuclear; D018000:Receptors, Peptide; D011994:Recombinant Proteins; D012269:Ribosomal Proteins; D000069816:SEC Translocation Channels; D018271:Signal Recognition Particle; C503637:Srp72 protein, mouse; C036318:signal peptide receptor; D006160:Guanosine Triphosphate; D020558:GTP Phosphohydrolases