Download MendeleyUncoupling conformational change from GTP hydrolysis in a heterotrimeric G protein {alpha}-subunit.
Thomas, C.J., Du, X., Li, P., Wang, Y., Ross, E.M., Sprang, S.R.(2004) Proc Natl Acad Sci U S A 101: 7560-7565
- PubMed: 15128951
- DOI: https://doi.org/10.1073/pnas.0304091101
- Primary Citation of Related Structures:
1SVK, 1SVS - PubMed Abstract:
Heterotrimeric G protein alpha (G alpha) subunits possess intrinsic GTPase activity that leads to functional deactivation with a rate constant of approximately 2 min(-1) at 30 degrees C. GTP hydrolysis causes conformational changes in three regions of G alpha, including Switch I and Switch II. Mutation of G202-->A in Switch II of G alpha(i1) accelerates the rates of both GTP hydrolysis and conformational change, which is measured by the loss of fluorescence from Trp-211 in Switch II. Mutation of K180-->P in Switch I increases the rate of conformational change but decreases the GTPase rate, which causes transient but substantial accumulation of a low-fluorescence G alpha(i1).GTP species. Isothermal titration calorimetric analysis of the binding of (G202A)G alpha(i1) and (K180P)G alpha(i1) to the GTPase-activating protein RGS4 indicates that the G202A mutation stabilizes the pretransition state-like conformation of G alpha(i1) that is mimicked by the complex of G alpha(i1) with GDP and magnesium fluoroaluminate, whereas the K180P mutation destabilizes this state. The crystal structures of (K180P)G alpha(i1) bound to a slowly hydrolyzable GTP analog, and the GDP.magnesium fluoroaluminate complex provide evidence that the Mg(2+) binding site is destabilized and that Switch I is torsionally restrained by the K180P mutation. The data are consistent with a catalytic mechanism for G alpha in which major conformational transitions in Switch I and Switch II are obligate events that precede the bond-breaking step in GTP hydrolysis. In (K180P)G alpha(i1), the two events are decoupled kinetically, whereas in the native protein they are concerted.
Organizational Affiliation:
Howard Hughes Medical Institute and Department of Biochemistry, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-9050, USA.
