RESUMO
The formation and analysis of amyloid fibers by two ß-glucosidases, BglA and BglB, belonging to the GH1 enzyme family, are reported. Both proteins have the (ß/α)8 TIM-barrel fold, which is characteristic of this family and is also the most common protein structure. BglA is an octamer, whereas BglB is a monomer. Amyloid fibrillation using pH and temperature as perturbing agents was investigated using fluorescence spectroscopy as a preliminary approach and corroborated using wide-field optical microscopy, confocal microscopy, and field-emission scanning electron microscopy. These analyses showed that both enzymes fibrillate at a wide range of acidic and alkaline conditions and at several temperature conditions, particularly at acidic pH (3-4) and at temperatures between 45 and 65 °C. Circular dichroism spectroscopy corroborated the transition from an α-helix to a ß-sheet secondary structure of both proteins in conditions where fibrillation was observed. Overall, our results suggest that fibrillation is a rather common phenomenon caused by protein misfolding, driven by a transition from an α-helix to a ß-sheet secondary structure, that many proteins can undergo if subjected to conditions that disturb their native conformation.
Assuntos
Amiloide , Amiloide/química , Amiloide/metabolismo , Concentração de Íons de Hidrogênio , Glicosídeo Hidrolases/química , Glicosídeo Hidrolases/metabolismo , Dicroísmo Circular , Temperatura , Estrutura Secundária de Proteína , Dobramento de ProteínaRESUMO
Previously, we applied in vitro evolution to generate the thermoresistant triple mutant H62R/N223Y/M319I of ß-glucosidase B (BglB) from Paenibacillus polymyxa. In order to dissect the energetic contributions to protein stabilization achieved by these mutations, we measured the kinetic constants of the heat denaturation of wild type BglB, the triple mutant and the three single mutants (H62R, N223Y, M319I) by circular dichroism at various temperatures. Our results show that all four mutants delayed the denaturation process. Based on the Transition State theory, the increase of the activation barrier for the thermal denaturation of the triple mutant (ΔΔG ( NâTS )) is equivalent to that produced by the sum of the contributions from the three single mutants, whose C ( ß ) s are located at least 18 Å apart. This analysis provides a formal demonstration of the generally accepted idea that protein thermal stability can be increased through sequential addition of individual mutations. Each of the mutations described here contribute in part to the overall effect, which in this case affects the unfolding barrier.
Assuntos
Paenibacillus/enzimologia , beta-Glucosidase/química , beta-Glucosidase/metabolismo , Substituição de Aminoácidos , Proteínas de Bactérias/química , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Dicroísmo Circular , Estabilidade Enzimática , Cinética , Modelos Moleculares , Mutação , Paenibacillus/genética , Desnaturação Proteica , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Relação Estrutura-Atividade , Termodinâmica , beta-Glucosidase/genéticaRESUMO
The fungus Phanerochaete flavido-alba is highly efficient in the oxidation of olive oil wastewater-derived polyphenols. This capability is largely due to the action of a multicopper-oxidase (MCO), encoded by the pfaL gene. We describe the sequence and organization of pfaL gene and the biochemical characterization and predicted 3D structural model of the encoded protein. pfaL gene organization and peptide sequence are highly similar to those of P. chrysosporium MCOs. However, PfaL is the first MCO in the Phanerochaete genus to show evident laccase activity. Phylogenetic analysis places PfaL in a differentiated sub-branch of ferroxidases. Protein structure analysis reveals close similarity of PfaL and ferroxidases and provides clues about the differences of activity between both types of enzymes. To summarize, P. flavido-alba laccase is the first enzyme in the novel and biochemically poorly defined group of "ferroxidases/laccases" that shows efficacious oxidation of laccase substrates, biotechnologically exploitable in bioremediation approaches.