title: Kinetic Mechanism of Formation of Hyperactive Embryonic Ras in Cells.
abstract: Embryonic Ras (ERas)--a new subset of Ras proteins--are characterized by a unique p-loop residue, unique Switch II residues, and an unusual extended N-terminus. When expressed, both murine and human ERas are highly populated in their GTP-bound forms. The expression of murine ERas is linked to the development of murine embryonic cells, and the expression of human ERas is correlated to certain human cancers. Mutation-based kinetic analyses, in combination with assessments of the kinetic parameter-based calculation of the fraction of the GTP-bound active form of ERas proteins, explain the kinetic mechanism that produces the unprecedented hyperactive ERas. The ERas-specific p-loop residue contributes ERas proteins to intrinsically populate their GTP-bound form in cells. Furthermore, the ERas-specific Switch II residues block the catalytic action of p120GAP on ERas proteins. This blockage sustains the previously mentioned GTP-bound ERas proteins. In essence, the combined work of the ERas-specific p-loop and Switch II residues populates the exceedingly high GTP-bound form of ERas in cells. This study also rules out any kinetic function of the unique ERas-specific N-terminus in the production of the hyperactive GTP-bound ERas in cells. The biological role of this N-terminus remains uninvestigated. Intriguingly, the ERas-specific p-loop residue matches the mutated Ser residue of the Costello Syndrome G12S HRas mutant that also intrinsically populates its GTP-bound form in cells. However, because the effector protein of ERas differs from that of G12S HRas, this kinetic similarity does not confer on ERas biological and/or pathophysiological similarity to G12S HRas.
authors.affiliation: Department of Chemistry and Biochemistry, The University of Texas at Arlington , Arlington, Texas 76019, United States.
authors.forename: Michael
authors.initials: M
authors.lastname: Wey
authors.affiliation: Department of Life Science, Sogang University , Seoul 121-742, Korea.
authors.forename: Jungwoon
authors.initials: J
authors.lastname: Lee
authors.affiliation: Department of Life Science, Sogang University , Seoul 121-742, Korea.
authors.forename: Hyo Sun
authors.initials: HS
authors.lastname: Kim
authors.affiliation: Humanzyme , 2201 West Campbell Park Drive, Chicago, Illinois 60612, United States.
authors.forename: Soon Seog
authors.initials: SS
authors.lastname: Jeong
authors.affiliation: Department of Life Science, Sogang University , Seoul 121-742, Korea.
authors.forename: Jungho
authors.initials: J
authors.lastname: Kim
authors.affiliation: Department of Chemistry and Biochemistry, The University of Texas at Arlington , Arlington, Texas 76019, United States.
authors.forename: Jongyun
authors.initials: J
authors.lastname: Heo
mesh_terms: D000818:Animals; D004622:Embryo, Mammalian; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D006868:Hydrolysis; D007700:Kinetics; D051379:Mice; D009154:Mutation; D041681:NIH 3T3 Cells; D011485:Protein Binding; D020729:p120 GTPase Activating Protein / Q000378:metabolism; D018631:ras Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D020662:Guanine Nucleotide Exchange Factors; D020729:p120 GTPase Activating Protein; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; D018631:ras Proteins