Structural and Thermal Stability Characterization of Escherichia coli D-Galactose/D-Glucose-Binding Protein

The effect of temperature and glucose binding on the structure of the galactose/glucose-binding protein from Escherichia coli was investigated by circular dichroism, Fourier transform infrared spectroscopy, and steady-state and time-resolved fluorescence. The data showed that the glucose binding induces a moderate change of the secondary structure content of the protein and increases the protein thermal stability. The infrared spectroscopy data showed that some protein stretches, involved in (alpha)-helices and (beta) strand conformations, are particularly sensitive to temperature. The fluorescence studies showed that the intrinsic tryptophanyl fluorescence of the protein is well represented by a three-exponential model and that in the presence of glucose the protein adopts a structure less accessible to the solvent. The new insights on the structural properties of the galactose/glucose-binding protein can contribute to a better understanding of the protein functions and represent fundamental information for the development of biotechnological applications of the protein.