Adsorption of an endoglucanase from the hyperthermophilic Pyrococcus furiosus on hydrophobic (polystyrene) and hydrophilic (silica) surfaces increases protein heat stability

The interaction of an endoglucanase from the hyperthermophilic microorganism Pyrococcus furiosus with two types of surfaces, that is, hydrophobic polystyrene and hydrophilic silica, was investigated, and the adsorption isotherms were determined. The adsorbed hyperthermostable enzyme did not undergo loss of biological activity. A model was proposed for the mechanism of interaction of the enzyme with the surface based on the shape of the adsorption isotherm, the morphological characteristics of the enzyme, and the thermodynamic parameters of the system. The enzyme was irreversibly immobilized at the solid/liquid interface even at high temperatures, and most interestingly, it acquired further heat stabilization upon adsorption. The denaturation temperature increased from 108 degrees C in solution to 116 degrees C upon adsorption on hydrophilic silica particles. Adsorption on the hydrophobic polystyrene surface even shifted the denaturation temperature to 135 degrees C, the most extreme experimentally determined protein denaturation temperature ever reported. Maintenance of the biological function particularly at high temperatures is important for the development of solid substrate immobilized enzymes for applications in biocatalysis and biotechnology. This also presents an additional stabilization mechanism employed by nature where the extracellular hyperthermostable enzyme remains folded and active at the extreme temperatures of its natural environment by adsorption on the surface of rocks and other materials appearing in the surroundings of the microorganism.