A Hyperthermophilic Protein Acquires Function at the Cost of Stability
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- 作者：Atsushi Mukaiyama ; Mitsuru Haruki ; Motonori Ota ; Yuichi Koga ; Kazufumi Takano ; and ; Shigenori Kanaya
- 刊名：Biochemistry
- 出版年：2006
- 出版时间：October 24, 2006
- 年：2006
- 卷：45
- 期：42
- 页码：12673 - 12679
- 全文大小：117K
- 年卷期：v.45,no.42(October 24, 2006)
- ISSN：1520-4995
文摘
Active-site residues are not often optimized for conformational stability (activity-stabilitytrade-offs) in proteins from organisms that grow at moderate temperature. It is unknown if the activity-stability trade-offs can be applied to proteins from hyperthermophiles. Because enzymatic activity usuallyincreases at higher temperature and hyperthermophilic proteins need high conformational stability, theymight not sacrifice the stability for their activity. This study attempts to clarify the contribution of active-site residues to the conformational stability of a hyperthermophilic protein. We therefore examined thethermodynamic stability and enzymatic activity of wild-type and active-site mutant proteins (D7N, E8A,E8Q, D105A, and D135A) of ribonuclease HII from Thermococcus kodakaraensis (Tk-RNase HII).Guanidine hydrochloride (GdnHCl)-induced denaturation was measured with circular dichroism at 220nm, and heat-induced denaturation was studied with differential scanning calorimetry. Both GdnHCl-and heat-induced denaturation were highly reversible in these proteins. All the mutations of these active-site residues, except that of Glu8 to Gln, reduced the enzymatic activity dramatically but increased theprotein stability by 7.0 to 11.1 kJ mol-1 at 50 
C. The mutation of Glu8 to Gln did not seriously affectthe enzymatic activity and increased the stability only by 2.5 kJ mol-1 at 50 C. These results indicatethat hyperthermophilic proteins also exhibit the activity-stability trade-offs. Therefore, the architecturalmechanism for hyperthermophilic proteins is equivalent to that for proteins at normal temperature.
C. The mutation of Glu8 to Gln did not seriously affectthe enzymatic activity and increased the stability only by 2.5 kJ mol-1 at 50 C. These results indicatethat hyperthermophilic proteins also exhibit the activity-stability trade-offs. Therefore, the architecturalmechanism for hyperthermophilic proteins is equivalent to that for proteins at normal temperature.