RESUMO
Aldose reductase (ALR2) has received considerable attention due to its possible link to long-term diabetic complications. Although crystal structures and kinetic data reveal important aspects of the reaction mechanism, details of the catalytic step are still unclear. In this paper a computer simulation study is presented that utilizes the hybrid quantum mechanical and molecular mechanical (QM-MM) potential to elucidate the nature of the hydride and proton transfer steps in the reduction of D-glyceraldehyde by ALR2. Several reaction pathways were investigated in two models with either Tyr48 or protonated His110+ acting as the potential proton donor in the active site. Calculations show that the substrate binds to ALR2 through hydrogen bonds in an orientation that facilitates the stereospecific catalytic step in both models. It is established that in the case that His110 is present in the protonated form in the native complex, it is the energetically favored proton donor compared with Tyr48 in the active pocket with neutral His110. The reaction mechanisms in the different models are discussed based on structural and energetic considerations.
Assuntos
Aldeído Redutase/química , Aldeído Redutase/metabolismo , Catálise , Domínio Catalítico , Metabolismo Energético , Gliceraldeído/química , Humanos , Modelos Moleculares , Oxirredução , Eletricidade Estática , EstereoisomerismoRESUMO
Self-organizing molecular field analysis (SOMFA) is a novel technique for three-dimensional quantitative structure-activity relations (3D-QSAR). It is simple and intuitive in concept and avoids the complex statistical tools and variable selection procedures favored by other methods. Our calculations show the method to be as predictive as the best 3D-QSAR methods available. Importantly, steric and electrostatic maps can be produced to aid the molecular design process by highlighting important molecular features. The simplicity of the technique leaves scope for further development, particularly with regard to handling molecular alignment and conformation selection. Here, the method has been used to predict the corticosteroid-binding globulin binding affinity of the "benchmark" steroids, expanded from the usual 31 compounds to 43 compounds. Test predictions have also been performed on a set of sulfonamide endothelin inhibitors.
Assuntos
Desenho de Fármacos , Modelos Moleculares , Endotelinas/antagonistas & inibidores , Esteroides/química , Relação Estrutura-Atividade , Sulfonamidas/química , Transcortina/químicaRESUMO
A model of the structure of erythropoietin (Epo) is presented based on structural homology to other hemopoietic cytokines. A model of the erythropoietin receptor complex was made based on evidence that this includes a homodimer of the receptor chain with known sequence. Key interactions are noted which explain data from mutation experiments, although at not all residues believed to be important to binding of Epo are at the interface. This is consistent with the hypothesis that the Epo receptor complex includes proteins in addition to the cloned receptor chain that have been cross-linked to Epo (Todokoro et al., Proc. Natl. Acad. Sci. USA 84:4126-4130, 1987; Mayeux et al., J. Biol. Chem. 266:23380-23385, 1991) but not isolated.
Assuntos
Eritropoetina/química , Modelos Moleculares , Receptores da Eritropoetina/química , Sequência de Aminoácidos , Animais , Sítios de Ligação/genética , Citocinas/química , Citocinas/genética , Eritropoetina/genética , Humanos , Ligação de Hidrogênio , Substâncias Macromoleculares , Dados de Sequência Molecular , Estrutura Molecular , Mutação , Receptores de Citocinas/química , Receptores de Citocinas/genética , Receptores da Eritropoetina/genética , Homologia de Sequência de AminoácidosRESUMO
A model for the structure of the cytokine interleukin-3 (IL-3) is presented based on the structural homology of the hematopoietic cytokines and utilizing the crystal structures of interleukin-5 and granulocyte macrophage colony stimulating factor (GM-CSF). In addition, models of the receptor complexes of GM-CSF and IL-3 are presented based on the structural homology of the hematopoietic receptors to growth hormone. Several key interactions between the ligands and their receptors are discovered, some in agreement with previous mutagenesis studies and others that have not yet been the subject of mutagenesis studies. The models provide insights into the binding of GM-CSF and IL-3 to their receptors.
Assuntos
Fator Estimulador de Colônias de Granulócitos e Macrófagos/química , Interleucina-3/química , Estrutura Secundária de Proteína , Receptores de Fator Estimulador das Colônias de Granulócitos e Macrófagos/química , Receptores de Fator Estimulador das Colônias de Granulócitos e Macrófagos/metabolismo , Receptores de Interleucina-3/química , Receptores de Interleucina-3/metabolismo , Sequência de Aminoácidos , Sítios de Ligação , Cristalografia por Raios X , Fator Estimulador de Colônias de Granulócitos e Macrófagos/metabolismo , Hormônio do Crescimento/química , Humanos , Interleucina-3/metabolismo , Modelos Moleculares , Modelos Estruturais , Dados de Sequência Molecular , Homologia de Sequência de AminoácidosRESUMO
Electrochemical characteristics of dopamine, ascorbic acid, and ferrocyanide measured with carbon-Nujol paste electrodes (CPEs) and stearate-modified carbon paste electrodes (SMEs) before and after treatment with either surfactant (Triton-X), lipid (phosphatidylethanolamine), or brain tissue indicate that the lipophilic nature of the brain destroys the selectivity of SMEs for dopamine by removing the hydrophobic elements from the electrode surface. Measurements of the degree and time-course of changes in surface capacitance of SMEs following contact with surface-active agents support this conclusion. The results suggest that SMEs cannot be used to detect dopamine unambiguously in vivo and emphasize the need to characterize electrochemical sensors in an environment similar to that of intended applications.
