The in situ observation of the temperature and pressure stability of recombinant Aspergillus aculeatus pectin methylesterase with Fourier transform IR spectroscopy reveals an unusual pressure stability of β-helices

The stability of recombinant Aspergillus aculeatus PME (pectin methylesterase), an enzyme with high β-helix content, was studied as a function of pressure and temperature. The conformational stability was monitored using FTIR (Fourier transform IR) spectroscopy whereas the functional enzyme stability was monitored by inactivation studies. Protein unfolding followed by amorphous aggregation, which makes the process irreversible, was observed at temperatures above 50 °C. This could be correlated to the irreversible enzyme inactivation observed at that temperature. Hydrostatic pressure greater than 1 GPa was necessary to induce changes in the enzyme's secondary structure. No enzyme inactivation was observed at up to 700 MPa. Pressure increased PME stability towards thermal denaturation. At 200 MPa, temperatures above 60 °C were necessary to cause significant PME unfolding and loss of activity. These results may be relevant for an understanding of the extreme stability of amyloid fibrils for which β-helices have been proposed as a structural element.