title: Analysis of Ras:RasGEF interactions by phage display and static multi-angle light scattering.
abstract: Molecular switches such as small GTPases of the Ras family cycle between inactive GDP-bound and active GTP-bound states. Their essential role in controlling development and cell homeostasis requires mechanisms which determine amplitude and timing of activation. This is achieved in part by the action of guanine nucleotide exchange factors, which function as highly controlled enzymes whose activity relies on spatial segregation and intra- and intermolecular regulation. Here, we describe two experimental methodologies that permit the identification and characterization of GTPase binding sites on activators by assaying complex formation within a broad range of affinities. In the first assay system, proteins presented on the surface of filamentous phage are used to probe affinity determinants of protein-protein interactions. In this application, a protein-displayed phage library is generated by random mutagenesis and a plate-based selection is performed to identify mutations that confer higher binding affinity to an immobilized target. The second method uses light scattering as a tool for measuring the molecular weight, stoichiometry, and polydispersity of protein complexes in solution. In this application, conventional gel filtration chromatography provides initial fractionation, and in-line light scattering measurements allow accurate determination of molar masses of the eluent. This technique also provides information about conformational homogeneity which can be used as a quality
authors.affiliation: Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA.
authors.forename: Holger
authors.initials: H
authors.lastname: Sondermann
authors.forename: Chen
authors.initials: C
authors.lastname: Zhao
authors.forename: Dafna
authors.initials: D
authors.lastname: Bar-Sagi
mesh_terms: D000818:Animals; D002850:Chromatography, Gel / Q000379:methods; D006801:Humans; D008027:Light; D019151:Peptide Library; D025941:Protein Interaction Mapping / Q000295:instrumentation / Q000379:methods*; D012542:Scattering, Radiation; D020663:ras Guanine Nucleotide Exchange Factors / Q000032:analysis / Q000378:metabolism*; D018631:ras Proteins / Q000032:analysis / Q000378:metabolism*
chemical_list: D019151:Peptide Library; D020663:ras Guanine Nucleotide Exchange Factors; D018631:ras Proteins