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Published December 1, 2001 | public
Journal Article

Role of SRP RNA in the GTPase Cycles of Ffh and FtsY


The bacterial homologues of the signal recognition particle (SRP) and its receptor, the Ffh•4.5S RNA ribonucleoprotein complex and the FtsY protein, respectively, form a unique complex in which both Ffh and FtsY act as GTPase activating proteins for one another, resulting in the mutual stimulation of GTP hydrolysis by both proteins. Previous work showed that 4.5S RNA enhances the GTPase activity in the presence of both Ffh and FtsY, but it was not clear how this was accomplished. In this work, kinetic and thermodynamic analyses of the GTPase reactions of Ffh and FtsY have provided insights into the role of 4.5S RNA in the GTPase cycles of Ffh and FtsY. We found that 4.5S RNA accelerates the association between Ffh and FtsY 400-fold in their GTP-bound form, analogous to its 200-fold catalytic effect on Ffh•FtsY association previously observed with the GppNHp-bound form [Peluso, P., et al. (2000) Science 288, 1640−1643]. Further, Ffh−FtsY association is rate-limiting for the observed GTPase reaction with subsaturating Ffh and FtsY, thereby accounting for the apparent stimulatory effect of 4.5S RNA on the GTPase activity observed previously. An additional step, GTP hydrolysis from the Ffh•FtsY complex, is also moderately facilitated by 4.5S RNA. These results suggest that 4.5S RNA modulates the conformation of the Ffh•FtsY complex and may, in turn, regulate its GTPase activity during the SRP functional cycle.

Additional Information

© 2001 American Chemical Society. Received August 9, 2001; Revised Manuscript Received October 12, 2001. This work is supported by NIH Grants GM 32384 to P.W. and GM 26494 to D.H. P.W. is an Investigator of the Howard Hughes Medical Institute, and S.S. is a Cancer Research Fund Fellow of the Damon Runyon-Walter Winchell Foundation. We thank C. Murphy for help with setting up the stopped-flow experiments, A. E. Johnson for advice in fluorescence experiments and for communications of unpublished data, D. Freymann for the expression plasmid for Ffh, and members of the Walter lab for comments on the manuscript.

Additional details

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October 18, 2023