RESUMO
Src family kinases are central regulators of a large number of signaling pathways. To adapt to the idiosyncrasies of different cell types, these kinases may need a fine-tuning of their intrinsic molecular control mechanisms. Here, we describe on a molecular level how the Fyn kinase uses alternative splicing to adapt to different cellular environments. Using structural analysis, site-directed mutagenesis, and functional analysis, we show how the inclusion of either exon 7A or 7B affects the autoinhibition of Fyn and how this changes the SH3-dependent interaction and tyrosine phosphorylation of Sam68, with functional consequences for the Sam68-regulated survival of epithelial cells. Our results illustrate a novel mechanism of evolution that may contribute to the complexity of Src kinase regulation.
Assuntos
Processamento Alternativo , Proteínas Proto-Oncogênicas c-fyn/antagonistas & inibidores , Proteínas Proto-Oncogênicas c-fyn/metabolismo , Proteínas Adaptadoras de Transdução de Sinal/genética , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Sequência de Aminoácidos , Animais , Apoptose/fisiologia , Linhagem Celular , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Evolução Molecular , Éxons , Humanos , Isoenzimas/antagonistas & inibidores , Isoenzimas/genética , Isoenzimas/metabolismo , Dados de Sequência Molecular , Mutagênese Sítio-Dirigida , Proteínas Proto-Oncogênicas c-fyn/genética , Proteínas de Ligação a RNA/genética , Proteínas de Ligação a RNA/metabolismo , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/metabolismo , Alinhamento de Sequência , Transdução de Sinais/fisiologia , Distribuição Tecidual , Proteína bcl-X/genética , Proteína bcl-X/metabolismo , Domínios de Homologia de srcRESUMO
The transacting transcriptional activator (Tat) is a viral protein essential for activation of the human immunodeficiency virus (HIV) genes, and it plays an important role in HIV induced immunodeficiency. We report the NMR structural characterization of the active Tat Mal variant that belongs to a highly virulent D-subtype HIV type-1 (HIV-1) strain (Mal) found mainly in Africa. A full Tat Mal protein (87 residues) is synthesized. This synthetic protein is active in a transactivation assay with HeLa cells infected with the HIV long terminal repeated noncoding sequences of the HIV-1 provirus (LTR) lac Z gene. Homonuclear (1)H-NMR spectra allows the sequential assignment of the Tat Mal spin systems. Simulating annealing generates 20 conformers with similar folding. The geometry of the mean structure is optimized with energy minimization to obtain a final structure. As the European variant (Tat Bru) the N-terminal region of Tat Mal constitutes the core, and there is a hydrophobic pocket composed of the conserved Trp 11 interacting with several aromatic residues. The two functional regions of Tat (basic and the cysteine-rich regions) are well exposed to the solvent. A short alpha-helix is observed in region V adjacent to the basic region. This alpha helix induces local structural variations compared to the NMR structure of Tat Bru, and it brings the cysteine-rich and basic regions closer. This study suggests that similar folding exists among Tat variants.
Assuntos
Produtos do Gene tat/química , HIV-1/química , África , Sequência de Aminoácidos , Europa (Continente) , Produtos do Gene tat/genética , Variação Genética , HIV-1/classificação , HIV-1/genética , Humanos , Hidrogênio/química , Modelos Moleculares , Dados de Sequência Molecular , Estrutura Molecular , Ressonância Magnética Nuclear Biomolecular , Conformação Proteica , Dobramento de Proteína , Produtos do Gene tat do Vírus da Imunodeficiência HumanaRESUMO
Tat is a viral protein essential for activation of the HIV genes and plays an important role in the HIV-induced immunodeficiency. We chemically synthesized a Tat protein (86 residues) with its six glycines C alpha labelled with 13C. This synthetic protein has the full Tat activity. Heteronuclear nuclear magnetic resonance (NMR) spectra and NOE back-calculation made possible the sequential assignment of the 86 spin systems. Consequently, 915 NMR restraints were identified and 272 of them turned out to be long range ([i-j] > 4), providing structural information on the whole Tat protein. The poor spectral dispersion of Tat NMR spectra does not allow an accurate structure to be determined as for other proteins studied by 2D NMR. Nevertheless, we were able to determine the folding for Tat protein at a 1-mM protein concentration in a 100 mM, pH 4.5 phosphate buffer. The two main Tat functional regions, the basic region and the cysteine-rich region, are well exposed to solvent while a part of the N-terminal region and the C-terminal region constitute the core of Tat Bru. The basic region adopts an extended structure while the cysteine-rich region is made up of two loops. Resolution of this structure was determinant to develop a drug design approach against Tat. The chemical synthesis of the drugs allowed the specific binding and the inhibition of Tat to be verified.