Coherent Experimental and Simulation Approach To Explore the Underlying Mechanism of Denaturation of Stem Bromelain in Osmolytes

Characterization of a protein in the context of its environment is of crucial importance for a complete understanding of its function. Although biophysical techniques provide powerful tools for studying the stability and activity of the enzyme in the presence of various cosolvents, an approach of combining both experimental techniques and molecular dynamic (MD) simulations may lead to the mechanistic insight into the interactions governing the stability of an enzyme. The knowledge of these interactions can be further utilized for range of modifications in the wild form of an enzyme for various pharmaceutical applications. Herein, we employed florescence, UV visible, circular dichroism (CD), dynamic light scattering (DLS) study, and MD simulations for comprehensive understanding of stem bromelain (BM) in the presence of betaine; sarcosine, arginine, and proline. The thermal stability of BM in the presence of 1 M of osmolytes is found to be in order: proline > betaine > buffer > arginine > sarcosine. BM gets more preferentially hydrated in the presence of betaine and proline than in sarcosine and arginine. Nonetheless, MD simulations suggest that betaine, sarcosine, and arginine at 1 M interact with the active site of BM through H-bonding except proline which are responsible for more disruption of active site. The distances between the catalytic site residues are 1.6, 1.9, 4.3, 5.0, and 6.2 angstrom for BM in proline, buffer, betaine, arginine, and sarcosine at 1 M, respectively. To the best of our knowledge, this is the first report on detailed unequivocal evidence of denaturation and deactivation of BM in the presence of methylamines and amino acids.