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A thermodynamic study of mesophilic, thermophilic, and hyperthermophilic L-arabinose isomerases: the effects of divalent metal ions on protein stability at elevated temperatures

 Dong-Woo Lee  ;  Young-Ho Hong  ;  Yu-Ryang Pyun  ;  Hae-Hun Shin  ;  Jong-Won Oh  ;  Han-Seung Lee  ;  Seong-Bo Kim  ;  Sang-Jae Lee  ;  Eun-Ah Choe 
 FEBS LETTERS, Vol.579(5) : 1261-1266, 2005 
Journal Title
Issue Date
Aldose-Ketose Isomerases/chemistry ; Aldose-Ketose Isomerases/metabolism* ; Bacillaceae/enzymology ; Bacillus/enzymology ; Cations, Divalent/pharmacology* ; Circular Dichroism ; Enzyme Stability/drug effects ; Guanidine/pharmacology ; Hot Temperature* ; Protein Denaturation/drug effects ; Protein Folding ; Thermodynamics ; Thermotoga maritima/enzymology ; Zinc/chemistry ; Zinc/pharmacology
L-Arabinose isomerase ; Unfolding ; Heat capacity ; Metal iron ; Structural stability
To gain insight into the structural stability of homologous homo-tetrameric l-arabinose isomerases (AI), we have examined the isothermal guanidine hydrochloride (GdnHCl)-induced unfolding of AIs from mesophilic Bacillus halodurans (BHAI), thermophilic Geobacillus stearothermophilus (GSAI), and hyperthermophilic Thermotoga maritima (TMAI) using circular dichroism spectroscopy. The GdnHCl-induced unfolding of the AIs can be well described by a two-state reaction between native tetramers and unfolded monomers, which directly confirms the validity of the linear extrapolation method to obtain the intrinsic stabilities of these proteins. The resulting unfolding free energy (ΔGU) values of the AIs as a function of temperature were fit to the Gibbs–Helmholtz equation to determine their thermodynamic parameters based on a two-state mechanism. Compared with the stability curves of BHAI in the presence and absence of Mn2+, those of holo GSAI and TMAI were more broadened than those of the apo enzymes at all temperatures, indicating increased melting temperatures (Tm) due to decreased heat capacity (ΔCp). Moreover, the extent of difference in ΔCp between the apo and holo thermophilic AIs is larger than that of BHAI. From these studies, we suggest that the metal dependence of the thermophilic AIs, resulting in the reduced ΔCp, may play a significant role in structural stability compared to their mesophilic analogues, and that the extent of metal dependence of AI stability seems to be highly correlated to oligomerization.
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1. College of Medicine (의과대학) > Dept. of Internal Medicine (내과학교실) > 1. Journal Papers
Yonsei Authors
Lee, Sang Jae(이상재)
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