Two conformational states of Ras GTPase exhibit differential GTP-binding kinetics

Biochem Biophys Res Commun. 2008 May 2;369(2):327-32. doi: 10.1016/j.bbrc.2008.01.169. Epub 2008 Feb 20.


Previous (31)P NMR studies revealed that small GTPases H-Ras and K-Ras in complex with GTP assume two interconverting conformational states, state 1 and state 2. While state 2 corresponds to an active conformation, little is known about the function of state 1, an inactive conformation incapable of effector binding. To address the biochemical properties of state 1, we measured the (31)P NMR spectra of five Ras family small GTPases; H-Ras, M-Ras, Rap1A, Rap2A and RalA, and find that they exhibit distinctive state 2/state 1 populations with the ratios ranging from 0.072 for M-Ras to 16 for Rap2A. Further, we show that GTPases with higher populations of state 1 exhibit higher dissociation and association rate constants for GTP. These results imply that GTP loading to the nucleotide-free small GTPases preferentially yields state 1, which is subsequently converted to state 2, rendering the GTP-bound form functional.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Binding Sites
  • Computer Simulation
  • Guanosine Triphosphate / chemistry*
  • Kinetics
  • Models, Chemical*
  • Models, Molecular*
  • Protein Binding
  • Protein Conformation
  • ras GTPase-Activating Proteins / chemistry*
  • ras GTPase-Activating Proteins / ultrastructure*


  • ras GTPase-Activating Proteins
  • Guanosine Triphosphate