Flexibility modulates the catalytic activity of a thermostable enzyme: key information from optical spectroscopy and molecular dynamics simulation.

Enzymes are dynamical macromolecules and their conformation can be altered via local fluctuations of side chains, large scale loop and even domain motions which are intimately linked to their function. Herein, we have addressed the role of dynamic flexibility in the catalytic activity of a thermostable enzyme almond beta-glucosidase (BGL). Optical spectroscopy and classical molecular dynamics (MD) simulation were employed to study the thermal stability, catalytic activity and dynamical flexibility of the enzyme. An enzyme assay reveals high thermal stability and optimum catalytic activity at 333 K. Polarization-gated fluorescence anisotropy measurements employing 8-anilino-1-napthelenesulfonic acid (ANS) have indicated increasing flexibility of the enzyme with an increase in temperature. A study of the atomic 3D structure of the enzyme shows the presence of four loop regions (LRs) strategically placed over the catalytic barrel as a lid. MD simulations have indicated that the flexibility of BGL increases concurrently with temperature through different fluctuating characteristics of the enzyme's LRs. Principal Component Analysis (PCA) and the Steered Molecular Dynamics (SMD) simulation manifest the gatekeeper role of the four LRs through their dynamic fluctuations surrounding the active site which controls the catalytic activity of BGL.