The research work has resulted in the development of original models to characterise protein thermal stability by differential scanning calorimetry, particularly when the protein undergoes irreversible thermal denaturation. This technique has been used to study several fragments of thermolysin.
Thermophilic enzymes are usually much more resistant to heat and most common protein denaturants than their counterparts from mesophilic sources and enzymes offer several specific advantages for biotechnological applications.
Research was carried out in order to characterize the functional, conformational and stability properties of enzymes isolated from thermophilic bacteria, in particular, from Thermotoga maritima, Sulfolobus solfataricus and Bacillus thermoproteolyticus. Relatively large scale fermentations, including optimization of the growth conditions of archaebacteria, were performed in order to isolate enzymes in suitable quantity. Many techniques (circular dichroism, fluorescence, nuclear magnetic resonance (NMR), calorimetry, ultracentrifugation, hydrogen deuterium exchange) were used to analyse the folding, association and stability of the newly isolated enzymes. A study was made of the independent folding of protein domains of thermolysin, with the view to establish the minimum size of a polypeptide chain able to fold into a stable globular structure.
Lactate dehydrogenase (LDH), glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and amylase were isolated from T maritima and their functional, association and stability properties investigated. LDH exhibits long term stability up to 85 C and GAPDH shows extreme stability, (transition point at 107 and 109 C for the apoenzymes and holoenzymes, respectively). Conformational studies were also carried out on alcohol dehydrogenase and beta-galactosidase from Sulfolobus. The molecular mechanism of protein degradation by proteolyic enzymes was investigated using thermolysin as a model, establishing that exposed and flexible loops are the vulnerable sites. The role of protein domains in folding and stability of proteins was examined by studying the conformational association and stability properties of C-terminal fragments of thermolysin.