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Stability of Haloalkaliphilic Geomicrobium sp. Protease Modulated by Salt

R. Karan and S. K. Khare*

Department of Chemistry, Indian Institute of Technology, Delhi, New Delhi, India; fax: +91-11-2658-1102; E-mail: skkhare@chemistry.iitd.ac.in; skhare@rocketmail.com

* To whom correspondence should be addressed.

Received October 21, 2010; Revision received December 30, 2010
A novel protease from the halophilic bacterium Geomicrobium sp. EMB2 (MTCC 10310) is described. The activity of the protease was modulated by salt, and it exhibited remarkable stability in organic solvents, at alkaline pH, and in other denaturing conditions. The structural changes under various denaturing conditions were analyzed by measurements of intrinsic fluorescence and circular dichroism spectroscopy. Circular dichroism showed that the secondary structure of the protease was predominantly α-helical but unfolded in salt-free medium. The structure is regained by inclusion of NaCl in the range of 2-5%. The presence of NaCl exerted a protective effect against thermal, organic solvent, and guanidine hydrochloride denaturation by preventing unfolding.
KEY WORDS: halophiles, solvent stability, protein folding, protease, circular dichroism, fluorescence

DOI: 10.1134/S0006297911060095