title: Molecular kinetics. Ras activation by SOS: allosteric regulation by altered fluctuation dynamics.
abstract: 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.
authors.affiliation: Howard Hughes Medical Institute, Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720, USA.
authors.forename: Lars
authors.initials: L
authors.lastname: Iversen
authors.affiliation: Howard Hughes Medical Institute, Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720, USA.
authors.forename: Hsiung-Lin
authors.initials: HL
authors.lastname: Tu
authors.affiliation: Howard Hughes Medical Institute, Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720, USA.
authors.forename: Wan-Chen
authors.initials: WC
authors.lastname: Lin
authors.affiliation: Howard Hughes Medical Institute, Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720, USA.
authors.forename: Sune M
authors.initials: SM
authors.lastname: Christensen
authors.affiliation: Department of Chemical Engineering, Massachusetts Institute of Technology (MIT), Cambridge, MA 02139, USA.
authors.forename: Steven M
authors.initials: SM
authors.lastname: Abel
authors.affiliation: Howard Hughes Medical Institute, Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA.
authors.forename: Jeff
authors.initials: J
authors.lastname: Iwig
authors.affiliation: Howard Hughes Medical Institute, Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720, USA.
authors.forename: Hung-Jen
authors.initials: HJ
authors.lastname: Wu
authors.affiliation: Howard Hughes Medical Institute, Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA.
authors.forename: Jodi
authors.initials: J
authors.lastname: Gureasko
authors.affiliation: Department of Mechanical Engineering, University of California, Berkeley, Berkeley, CA 94720, USA.
authors.forename: Christopher
authors.initials: C
authors.lastname: Rhodes
authors.affiliation: Howard Hughes Medical Institute, Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720, USA.
authors.forename: Rebecca S
authors.initials: RS
authors.lastname: Petit
authors.affiliation: Howard Hughes Medical Institute, Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720, USA.
authors.forename: Scott D
authors.initials: SD
authors.lastname: Hansen
authors.affiliation: Department of Chemistry, MIT, Cambridge, MA 02139, USA.
authors.forename: Peter
authors.initials: P
authors.lastname: Thill
authors.affiliation: Mechanobiology Institute, National University of Singapore, Singapore.
authors.forename: Cheng-Han
authors.initials: CH
authors.lastname: Yu
authors.affiliation: Department of Chemistry and Nano-Science Center, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Dimitrios
authors.initials: D
authors.lastname: Stamou
authors.affiliation: Department of Chemical Engineering, Massachusetts Institute of Technology (MIT), Cambridge, MA 02139, USA. Department of Chemistry, MIT, Cambridge, MA 02139, USA. Department of Biological Engineering, MIT, Cambridge, MA 02139, USA. Ragon Institute of Massachusetts General Hospital, MIT, and Harvard, Cambridge, MA 02139, USA. Department of Physics, MIT, Cambridge, MA 02139, USA. Institute for Medical Engineering and Science, MIT, Cambridge, MA 02139, USA.
authors.forename: Arup K
authors.initials: AK
authors.lastname: Chakraborty
authors.affiliation: Howard Hughes Medical Institute, Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720, USA. Howard Hughes Medical Institute, Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA. Physical Biosciences and Materials Sciences Divisions, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: John
authors.initials: J
authors.lastname: Kuriyan
authors.affiliation: Howard Hughes Medical Institute, Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720, USA. Mechanobiology Institute, National University of Singapore, Singapore. Physical Biosciences and Materials Sciences Divisions, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA. Berkeley Education Alliance for Research in Singapore, 1 Create Way, CREATE tower level 11, University Town, Singapore 138602. jtgroves@lbl.gov.
authors.forename: Jay T
authors.initials: JT
authors.lastname: Groves
mesh_terms: D000494:Allosteric Regulation; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D004789:Enzyme Activation; D006801:Humans; D007700:Kinetics; D009711:Nucleotides / Q000737:chemistry; D054730:Protein Interaction Domains and Motifs; D016283:Proto-Oncogene Proteins p21(ras) / Q000819:agonists*; D020839:Son of Sevenless Protein, Drosophila / Q000737:chemistry* / Q000235:genetics
chemical_list: D009711:Nucleotides; D020839:Son of Sevenless Protein, Drosophila; D016283:Proto-Oncogene Proteins p21(ras)