Structure and Dynamics of Cold-Adapted Enzymes as Investigated by FT-IR Spectroscopy and MD. The Case of an Esterase from Pseudoalteromonas haloplanktis

Psychrophiles are cold-adapted organisms that produce enzymes that display a high catalytic efficiency at low temperatures. In recent years, these low-temperature working enzymes have attracted the attention of scientists because of their peculiar properties that render them particularly useful in investigating the relationship between enzyme stability and flexibility. Recently, a new esterase was identified and isolated from the cold-adapted organism Pseudoalteromonas haloplanktis. The enzyme, denoted as PhEST, presents a dimeric structure with a molecular mass of 60 kDa. In this work, we used Fourier transform infrared spectroscopy and molecular dynamics simulations to investigate the functional and structural properties of PhEST over a wide range of temperature. The obtained results reveal that the structure of PhEST is quite stable up to 40 °C. In fact, the protein starts to denature at about 45 °C through the formation of new secondary structural elements such as intermolecular β-sheets. In addition, our results indicate that the flexibility of protein segment 55−65 (335−345 in subunit B), which corresponds to a loop near the active site of the enzyme, plays a crucial role in the protein function.