RESUMO
Following the paradigm set by STI571, protein tyrosine kinase inhibitors are emerging as a promising class of drugs, capable of modulating intracellular signaling and demonstrating therapeutic potential for the treatment of proliferative diseases. Although the majority of chronic phase CML patients treated with STI571 respond, some patients, especially those with more advanced disease, relapse. This article reviews the reasons for relapse and, in particular, analyses resistance resulting from Bcr-Abl tyrosine kinase domain mutations at the molecular level. Arguments are based upon the structure of the STI571-Abl complex, which is compared to the crystal structures of PD173955-Abl and PD180970-Abl, which bind to the kinase differently. Strategies to potentially circumvent or overcome resistance are discussed.
Assuntos
Antineoplásicos/uso terapêutico , Resistencia a Medicamentos Antineoplásicos/genética , Inibidores Enzimáticos/uso terapêutico , Leucemia Mielogênica Crônica BCR-ABL Positiva , Piperazinas/uso terapêutico , Proteínas Tirosina Quinases , Pirimidinas/uso terapêutico , Animais , Benzamidas , Proteínas de Fusão bcr-abl , Genes abl/genética , Humanos , Mesilato de Imatinib , Leucemia Mielogênica Crônica BCR-ABL Positiva/tratamento farmacológico , Leucemia Mielogênica Crônica BCR-ABL Positiva/enzimologia , Leucemia Mielogênica Crônica BCR-ABL Positiva/genética , Mutação , Proteínas Tirosina Quinases/antagonistas & inibidores , Proteínas Tirosina Quinases/genéticaRESUMO
The structure of a recombinant protein, TyrRS(delta4), corresponding to the anticodon arm binding domain of Bacillus stearothermophilus tyrosyl-tRNA synthetase, has been solved, and its dynamics have been studied by nuclear magnetic resonance (NMR). It is the first structure described for such a domain of a tyrosyl-tRNA synthetase. It consists of a five-stranded beta sheet, packed against two alpha helices on one side and one alpha helix on the other side. A large part of the domain is structurally similar to other functionally unrelated RNA binding proteins. The basic residues known to be essential for tRNA binding and charging are exposed to the solvent on the same face of the molecule. The structure of TyrRS(delta4), together with previous mutagenesis data, allows one to delineate the region of interaction with tRNATyr.
Assuntos
Anticódon , Geobacillus stearothermophilus/enzimologia , Estrutura Secundária de Proteína , Estrutura Terciária de Proteína , Tirosina-tRNA Ligase/química , Sequência de Aminoácidos , Cristalografia por Raios X , Geobacillus stearothermophilus/química , Espectroscopia de Ressonância Magnética , Modelos Moleculares , Dados de Sequência Molecular , RNA de Transferência/metabolismo , Proteínas de Ligação a RNA/química , Proteínas de Ligação a RNA/genética , Proteínas de Ligação a RNA/metabolismo , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Alinhamento de Sequência , Tirosina-tRNA Ligase/genética , Tirosina-tRNA Ligase/metabolismoRESUMO
To probe the role of individual disulfide bonds in the folding kinetics of hen lysozyme, the variants with two mutations, C30A,C115A, C64A,C80A, and C76A,C94A, were constructed. The corresponding proteins, each lacking one disulfide bond, were produced in Escherichia coli as inclusion bodies and solubilized, purified, and renatured/oxidized using original protocols. Their enzymatic, spectral, and hydrodynamic characteristics confirmed that their conformations were very similar to that of native wild-type (WT) lysozyme. Stopped-flow studies on the renaturation of these guanidine-unfolded proteins with their three disulfides intact showed that, for the three variants, the native far-UV ellipticity was regained in a burst phase within the 4-ms instrument dead-time. The transient overshoots of far-UV ellipticity and tryptophan fluorescence that follow the burst phase, as well as the kinetics of transient 8-anilino-1-naphthalene-sulfonic acid (ANS) binding, were diversely affected depending on the variant. Together with previous reports on the folding kinetics of WT lysozyme carboxymethylated on cysteines 6 and 127, detailed analysis of the kinetics showed that (1) none of the disulfide bonds were indispensable for the rapid formation (<4 ms) of the native-like secondary structure; (2) the two intra-alpha-domain disulfides (C6-C127 and C30-C115) must be simultaneously present to generate the trapped intermediate responsible for the slow folding population observed in WT lysozyme; and (3) the intra-beta-domain (C64-C80) and the inter-alphabeta-domains (C76-C94) disulfides do not affect the kinetics of formation of the trapped intermediate but are involved in its stability.
