Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published September 21, 2004 | Published
Journal Article Open

Mechanism of Association and Reciprocal Activation of Two GTPases


The signal recognition particle (SRP) mediates the cotranslational targeting of nascent proteins to the eukaryotic endoplasmic reticulum membrane or the bacterial plasma membrane. During this process, two GTPases, one in SRP and one in the SRP receptor (named Ffh and FtsY in bacteria, respectively), form a complex in which both proteins reciprocally activate the GTPase reaction of one another. Here, we explore by site-directed mutagenesis the role of 45 conserved surface residues in the Ffh-FtsY interaction. Mutations of a large number of residues at the interface impair complex formation, supporting the importance of an extensive interaction surface. Surprisingly, even after a stable complex is formed, single mutations in FtsY can block the activation of GTP hydrolysis in both active sites. Thus, activation requires conformational changes across the interface that coordinate the positioning of catalytic residues in both GTPase sites. A distinct class of mutants exhibits half-site reactivity and thus allows us to further uncouple the activation of individual GTPases. Our dissection of the activation process suggests discrete conformational stages during formation of the active SRP•SRP receptor complex. Each stage provides a potential control point in the targeting reaction at which regulation by additional components can be exerted, thus ensuring the binding and release of cargo at the appropriate time.

Additional Information

© 2004 Shan et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Received June 9, 2004; Accepted July 26, 2004; Published September 21, 2004. We thank Geeta J. Narlikar, Wallace Marshall, Pascal F. Egea, and Niels R. Bradshaw for helpful comments on the manuscript. This work was supported by National Institutes of Health grants to PW and RMS. PW is an investigator of the Howard Hughes Medical Institute. SS was a cancer research fund fellow of the Damon Runyon-Walter Winchell Foundation when this work began and is currently a Burroughs Wellcome Fund fellow. The authors have declared that no conflicts of interest exist. Author Contributions: SS and PW conceived and designed the experiments. SS performed the experiments. SS analyzed the data. SS contributed reagents/materials/analysis tools. SS, RMS, and PW wrote the paper.

Attached Files

Published - pbio.0020320.pdf


Files (326.1 kB)
Name Size Download all
326.1 kB Preview Download

Additional details

August 19, 2023
October 18, 2023