Chemical processing as a tool to generate ovalbumin variants with changed stability.

Processing of ovalbumin may result in proteins that differ more than 23 degrees C in denaturation temperature while the structural fold is not significantly affected. This is achieved by 1) conversion of positive residues into negative ones (succinylation); 2) elimination of negative charges (methylation); 3) reducing the proteins hydrophobic exposure (glycosylation); 4) increasing the hydrophobic exposure (lipophilization); or by 5) processing under alkaline conditions and elevated temperature (S-ovalbumin). The effect on the structural fold was investigated using a variety of biochemical and spectroscopic tools. The consequences of the modification on the thermodynamics of the protein was studied using differential scanning calorimetry and by monitoring the tryptophan fluorescence or ellipticity at 222 nm of protein samples dissolved in different concentrations of guanidine-HCl. The impact of the modification on the denaturation temperature scales for all types of modifications with a free energy change of about 1 kJ per mol ovalbumin per Kelvin (or 0.0026 kJ per mol residue per K). The nature of the covalently coupled moiety determines the impact of the modification on the protein thermodynamics. It is suggested that especially for lipophilized protein the water-binding properties are substantially lowered. Processing of globular proteins in a controlled manner offers great opportunities to control a desired functionality, for example, as texturizer in food or medical applications.