Molecular Switch for Signal Transduction: Structural Differences between Active and Inactive Forms of Protooncogenic ras Proteins

• Published in: Science (American Association for the Advancement of Science) 1990-02, Vol.247 (4945), p.939-945
• Main Authors: Milburn, Michael V., Tong, Liang, deVos, Abraham M., Brünger, Axel, Yamaizumi, Ziro, Nishimura, Susumu, Kim, Sung-Hou
• Format: Article
• Language: English
• Subjects: Amino acids; Binding Sites; Biochemistry; Biological and medical sciences; Biology; Cancer; Cancer cells; Cells; Cells (Biology); Crystal lattices; Crystal structure; Crystalline structure; Crystallization; Crystallography; Crystals; Fundamental and applied biological sciences. Psychology; Gross domestic product; Growth; Growth factors; Guanine nucleotides; Guanosine Diphosphate - metabolism; Guanosine Triphosphate - metabolism; Humans; Hydrolysis; Innovations; man; Models, Molecular; Molecular biophysics; Molecular Structure; Molecules; oncoproteins; Phosphates; Physiological regulation; Protein Conformation; Protein research; Proteins; Proto-Oncogene Proteins - metabolism; Proto-Oncogene Proteins p21(ras); Proto-oncogenes; ras; Research Article; Signal Transduction; Structure in molecular biology; Structure-Activity Relationship; Transduction; Transduction (Genetics); X-ray crystallography
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.2406906

$Ras$ proteins participate as a molecular switch in the early steps of the signal transduction pathway that is associated with cell growth and differentiation. When the protein is in its GTP complexed form it is active in signal transduction, whereas it is inactive in its GDP complexed form. A comparison of eight three-dimensional structures of $ras$ proteins in four different crystal lattices, five with a nonhydrolyzable GTP analog and three with GDP, reveals that the "on" and "off" states of the switch are distinguished by conformational differences that span a length of more than 40 Å, and are induced by the γ-phosphate. The most significant differences are localized in two regions: residues 30 to 38 (the switch I region) in the second loop and residues 60 to 76 (the switch II region) consisting of the fourth loop and the short α-helix that follows the loop. Both regions are highly exposed and form a continuous strip on the molecular surface most likely to be the recognition sites for the effector and receptor molecule(or molecules). The conformational differences also provide a structural basis for understanding the biological and biochemical changes of the proteins due to oncogenic mutations, autophosphorylation, and GTP hydrolysis, and for understanding the interactions with other proteins.