1 Administration, Department of Chemistry, Faculty of Science, Københavns Universitet2 Department of Chemistry, Faculty of Science, Københavns Universitet3 University of California4 Massachusetts Institute of Technology (MIT)5 National University of Singapore6 Department of Chemistry, Faculty of Science, Københavns Universitet7 National University of Singapore8 Administration, Department of Chemistry, Faculty of Science, Københavns Universitet
allosteric regulation by altered fluctuation dynamics
Activation of the small guanosine triphosphatase H-Ras by the exchange factor Son of Sevenless (SOS) is an important hub for signal transduction. Multiple layers of regulation, through protein and membrane interactions, govern activity of SOS. We characterized the specific activity of individual SOS molecules catalyzing nucleotide exchange in H-Ras. Single-molecule kinetic traces revealed that SOS samples a broad distribution of turnover rates through stochastic fluctuations between distinct, long-lived (more than 100 seconds), functional states. The expected allosteric activation of SOS by Ras-guanosine triphosphate (GTP) was conspicuously absent in the mean rate. However, fluctuations into highly active states were modulated by Ras-GTP. This reveals a mechanism in which functional output may be determined by the dynamical spectrum of rates sampled by a small number of enzymes, rather than the ensemble average.
Science (new York, N.y.), 2014, Vol 345, Issue 6192, p. 50-54
Allosteric Regulation; Catalytic Domain; Crystallography, X-Ray; Enzyme Activation; Humans; Kinetics; Nucleotides; Protein Interaction Domains and Motifs; Proto-Oncogene Proteins p21(ras); Son of Sevenless Protein, Drosophila