Structural and dynamical thermostability of psychrophilic enzyme at various temperatures: Molecular dynamics simulations of tryptophan synthase.

Mesophilic enzymes are among the most frequently used biocatalysts, however, psychrophilic enzymes are crucially important for their use in heat-sensitive reactions. How enzymes can work efficiently at various range of temperatures is an interesting subject for researchers, and yet it is very least explored. The structural and dynamical behavior of psychrophilic enzymes and their thermostability at various temperatures can help to understand the mechanism and function at molecular level, and for this purpose the ligand-free α-subunit of Shewanella frigidimarina's tryptophan synthase (Sf-TRPS) in isolated monomeric and in hetero-αβ-dimeric states was subjected to molecular dynamics (MD) simulations study. The simulation sampled a complete open conformation of Loop L6 in α-subunit with and without β-partner, which was further investigated under three temperatures mimicking psychrophilic, mesophilic and thermophilic environment. The results indicated an imperative role of β-subunit in the dynamics of L6 loop as well as in the thermostability of α-subunit by increasing interaction strength at the αβ-interface. An interesting relation was observed between the numbers of H-bonds and residue-pairs forming salt bridges at every temperature, and the combine effect seemed to regulate the balance between protein rigidity and flexibility. The outcome of the study will help to understand the driving forces that lead to the stability of the protein at different temperature, and thereby, assist in enzyme engineering that will be beneficial from industrial point of view.