RESUMO
Previously, we have demonstrated that the tyrosine phosphorylated hepatocyte growth factor receptor (Met) binds to the c-Cbl phosphotyrosine-recognition, tyrosine kinase binding (TKB) domain in a reverse orientation compared to other c-Cbl binding partners. A Met peptide with the DpYR motif changed to RpYD (MetRD) retains a similar TKB binding affinity as the native Met peptide. However, the TKB: MetRD complex crystal structure reveals a complete reversal of the binding orientation. Collated data indicates that both binding and orientation is dictated by the phosphorylated tyrosine and an adjacent arginine forming intra-peptide hydrogen bonds and aligning unidirectionally with complementary charges in the phosphotyrosine binding pocket of c-Cbl.
Assuntos
Arginina , Fosfotirosina , Proteínas Proto-Oncogênicas c-cbl/metabolismo , Proteínas Proto-Oncogênicas c-met/metabolismo , Receptores de Fatores de Crescimento/metabolismo , Motivos de Aminoácidos , Sequência de Aminoácidos , Cristalografia por Raios X , Humanos , Ligação de Hidrogênio , Cinética , Espectrometria de Massas , Ligação Proteica , Proteínas Proto-Oncogênicas c-met/química , Receptores de Fatores de Crescimento/química , Ressonância de Plasmônio de SuperfícieRESUMO
RNA methyltransferases (MTases) are important players in the biogenesis and regulation of the ribosome, the cellular machine for protein synthesis. RsmC is a MTase that catalyzes the transfer of a methyl group from S-adenosyl-l-methionine (SAM) to G1207 of 16S rRNA. Mutations of G1207 have dominant lethal phenotypes in Escherichia coli, underscoring the significance of this modified nucleotide for ribosome function. Here we report the crystal structure of E. coli RsmC refined to 2.1 A resolution, which reveals two homologous domains tandemly duplicated within a single polypeptide. We characterized the function of the individual domains and identified key residues involved in binding of rRNA and SAM, and in catalysis. We also discovered that one of the domains is important for the folding of the other. Domain duplication and subfunctionalization by complementary degeneration of redundant functions (in particular substrate binding versus catalysis) has been reported for many enzymes, including those involved in RNA metabolism. Thus, RsmC can be regarded as a model system for functional streamlining of domains accompanied by the development of dependencies concerning folding and stability.
Assuntos
Proteínas de Escherichia coli/química , Metiltransferases/química , Modelos Moleculares , Sequência de Aminoácidos , Aminoácidos/química , Biologia Computacional , Proteínas de Escherichia coli/metabolismo , Metiltransferases/metabolismo , Dados de Sequência Molecular , Estrutura Terciária de Proteína , S-Adenosilmetionina/química , Alinhamento de Sequência , Relação Estrutura-AtividadeRESUMO
Ehretianone (1), a new quinonoid xanthene, together with known sterols, was isolated from a MeOH extract of the root bark of Ehretia buxifolia. The structure of ehretianone was elucidated as 7-hydroxy-9a alpha-(3-methylbut-2-enyl)-4a alpha,9 alpha-(2-methylprop-2-enyl)-4a, 9a-dihydro-1,4-dioxoxanthene on the basis of spectroscopic data and X-ray crystallographic analysis. The antisnake venom activity of ehretianone against Echis carinatus venom in mice is also reported.