Effect of organic solvents on the structure and activity of moderately halophilic Bacillus sp. EMB9 protease.

Halophilic enzymes have been manifested for their stability and catalytic abilities under harsh operational conditions. These have been documented to withstand denaturation in presence of high temperature, pH, presence of organic solvents and chaotropic agents. The present study aims at understanding the stability and activity of a halophilic Bacillus sp. EMB9 protease in organic solvents. The protease was uniquely stable in polar solvents. A clear correlation was evident between the protease function and conformational transitions, validated by CD and fluorescence spectral studies. The study affirms that preservation of protein structure, possibly due to charge screening of the protein surface by Ca(2+) and Na(+) ions provides stability against organic solvents and averts denaturation. Salt was also found to exert a protective effect on dialyzed protease against chaotropism of solvents. Presence of 1 % (w/v) NaCl restored the activity in the dialyzed protease and prevented denaturation in methanol, toluene and n-decane. The work will have further implication on discerning protein folding in saline as well as non-aqueous environments.