Protective Effect of Biological Osmolytes against Heat- and Chaotropic Agent-Induced Denaturation of Bacillus licheniformis γ-Glutamyl Transpeptidase
2018
Huei-Fen Lo, Hungkuang University, Taichung, Taiwan | Meng-Chun Chi, National Chiayi University, Chiayi, China | Min-Guan Lin, Institute of Molecular Biology, Taipei, Taiwan | Yuan-Gin Lan, National Chiayi University, Chiayi, Taiwan | Tzu-Fan Wang, National Chiayi University, Chiayi, Taiwan | Long-Liu Lin, National Chiayi University, Chiayi, Taiwan
In the present study, the stabilizing effect of four different biological osmolytes on Bacillus licheniformis γ-glutamyl transpeptidase (BlGGT) was investigated. BlGGT appeared to be stable under temperatures below 40℃, but the enzyme retained less than 10% of its activity at 60℃. The tested osmolytes exhibited different degrees of effectiveness against temperature inactivation of BlGGT, and sucrose was found to be the most effective among these. The use of circular dichroism spectroscopy for studying the secondary structure of BlGGT revealed that the temperature-induced conformational change of the protein molecule could be prevented by the osmolytes. Consistently, the molecular structure of the enzyme was essentially conserved by the osmolytes at elevated temperatures as monitored by fluorescence spectroscopy. Sucrose was further observed to counteract guanidine hydrochloride (GdnHCl)- and urea-induced denaturation of BlGGT. Taken together, we observed evidently that some well-known biological osmolytes, especially sucrose, make a dominant contribution to the structural stabilization of BlGTT.
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