Dual Recognition of the Ribosome and the Signal Recognition Particle by the SRP Receptor during Protein Targeting to the Endoplasmic Reticulum

• Published in: The Journal of cell biology Vol. 162; no. 4; pp. 575 - 585
• Main Authors: Mandon, Elisabet C., Jiang, Ying, Gilmore, Reid
• Format: Journal Article
• Language: English
• Published: United States Rockefeller University Press 18.08.2003; The Rockefeller University Press
• Subjects: Animals; Biosensing techniques; Biosensors; Canines; Cellular biology; Dogs; Drug interactions; Endoplasmic reticulum; Endoplasmic Reticulum - metabolism; GTP Phosphohydrolases - metabolism; Hydrolysis; Kinetics; Microsomes; Protein transport; Proteins; Proteins - metabolism; Receptors; Receptors, Cytoplasmic and Nuclear - metabolism; Receptors, Peptide - metabolism; Ribosomal DNA; Ribosomes; Ribosomes - metabolism; Signal Recognition Particle - metabolism
• ISSN: 0021-9525; 1540-8140
• DOI: 10.1083/jcb.200303143

We have analyzed the interactions between the signal recognition particle (SRP), the SRP receptor (SR), and the ribosome using GTPase assays, biosensor experiments, and ribosome binding assays. Possible mechanisms that could contribute to an enhanced affinity between the SR and the SRP-ribosome nascent chain complex to promote protein translocation under physiological ionic strength conditions have been explored. Ribosomes or 60S large ribosomal subunits activate the GTPase cycle of SRP54 and SRα by providing a platform for assembly of the SRP-SR complex. Biosensor experiments revealed high-affinity, saturable binding of ribosomes or large ribosomal subunits to the SR. Remarkably, the SR has a 100-fold higher affinity for the ribosome than for SRP. Proteoliposomes that contain the SR bind nontranslating ribosomes with an affinity comparable to that shown by the Sec61 complex. An NH2-terminal 319-residue segment of SRα is necessary and sufficient for binding of SR to the ribosome. We propose that the ribosome-SR interaction accelerates targeting of the ribosome nascent chain complex to the RER, while the SRP-SR interaction is crucial for maintaining the fidelity of the targeting reaction.