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Published April 2013 | public
Journal Article

Activated GTPase movement on an RNA scaffold drives cotranslational protein targeting


Signal Recognition Particle (SRP) and its receptor (SR) are GTPases that translocate ribosome-nascent chain complexes (RNCs) from cytosol to cellular membranes. SRP recognizes the RNC, and through interactions with SR, brings the RNC to the membrane. Subsequent rearrangements activate GTP hydrolysis and load the RNC onto the translocon. During this process, the SRP RNA plays an indispensible role in stimulating both SRP-SR complex formation and the following GTP hydrolysis. Previous studies hinted that the SRP RNA is a bi-functional molecule with two distinct functional ends, the tetraloop end and the distal end, that each stimulates the SRP-SR complex formation and GTP hydrolysis steps. Here we used single molecule technique to directly visualize the global rearrangement of the GTPase complex from the RNA's tetraloop end to the distal end, traveling over 100 Angstrom in the targeting reaction. Moreover, we showed that the rearrangement is tightly controlled by the RNC and the translocon. This large-scale movement of the GTPase complex provides a molecular mechanism of coupling GTPase activation to the transfer of RNC, thereby ensuring productive protein targeting.

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© 2013 FASEB.

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