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 degrees C. In fact, the protein starts to denature at about 45 degrees C through the formation of new secondary structural elements such as intermolecular beta-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.