Effect of high hydrostatic pressure on the secondary structure of microbial transglutaminase

Enzyme activity and corresponding secondary structure, measured by circular dichroism was analysed before und after treatment of microbial transglutaminase at different temperatures (40, 80°C) and pressures (0.1, 200, 400, 600 MPa). Irreversible enzyme inactivation was achieved at 80°C after 2 minutes at atmospheric pressure. Enzyme inactivation at 0.1, 200, 400, 600 MPa and 40°C followed first order kinetics. Increasing pressure reduced MTG activity, nevertheless the enzyme showed a residual activity of 50% after 12 min at 600 MPa. The analysis of the native enzyme exhibited well-defined proportions between α-helix, β-strand, β-turn and unordered structures. In contrast to heating, high-pressure treatment only at high levels induced significant decrease in the α-helix content, whereas β-strand substructures remained unaltered in both cases. Based on the known crystal structure of MTG it can be concluded that the active centre of the enzyme itself, which is located in an expanded β-strand domain, is relatively stable and pressure-induced inactivation is caused by a degradation of α-helix elements with corresponding influence on the tertiary structure.