Thermodynamics and Structural Features of the Yeast Saccharomyces cerevisiae External Invertase Isoforms in Guanidinium-chloride Solutions

Abstract

Recently, four external invertase isoforms (EINV1, EINV2, EINV3, and EINV4) have been isolated from S. cerevisiae. However, there is nothing known about their structural features and thermodynamics of unfolding. Since this information is essential for understanding their functioning at the molecular level as well as applicable in the food industry, we investigated guanidinium-chloride induced structural changes of the isoforms by CD and fluorescence spectroscopy. The resulting unfolding curves measured for each isoform at different temperatures were described simultaneously by a reversible two-state model to obtain the corresponding thermodynamic parameters. Here, we show that they are different for different isoforms and demonstrate that they correlate with the surface charge density of the native isoforms which follows the order EINV1 LT EINV2 LT EINV3 LT EINV4. It appears that at physiological temperatures the thermodynamic stability of the isoforms follows the same order, while above 55 degrees C, the order is the opposite EINV1 > EINV2 > EINV3 approximate to EINV4. This suggests that increasing the efficiency of the food industry processes involving inverta,se would require the application of EINV3 and/or EINV4 at physiological temperatures and EINV1 at elevated temperatures.