Hydrophobic effect on the stability and folding of a hyperthermophilic protein.
Ribonuclease HII from hyperthermophile Thermococcus kodakaraensis (Tk-RNase HII) is a kinetically robust monomeric protein. The conformational stability and folding kinetics of Tk-RNase HII were measured for nine mutant proteins in which a buried larger hydrophobic side chain is replaced by a smaller one (Leu/Ile to Ala). The mutant proteins were destabilized by 8.9 to 22.0 kJ mol(-1) as compared with the wild-type protein. The removal of each -CH(2)- group burial decreased the stability by 5.1 kJ mol(-1) on average in the mutant proteins of Tk-RNase HII examined. This is comparable with the value of 5.3 kJ mol(-1) obtained from experiments for proteins from organisms growing at moderate temperature. We conclude that the hydrophobic residues buried inside protein molecules contribute to the stabilization of hyperthermophilic proteins to a similar extent as proteins at normal temperature. In the folding experiments, the mutant proteins of Tk-RNase HII examined exhibited faster unfolding compared with the wild-type protein. These results indicate that the buried hydrophobic residues strongly contribute to the kinetic robustness of Tk-RNase HII. This is the first report that provides a practical cause of slow unfolding of hyperthermostable proteins.
Dong
Hongju
H
Department of Material and Life Science, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan.
Mukaiyama
Atsushi
A
Tadokoro
Takashi
T
Koga
Yuichi
Y
Takano
Kazufumi
K
Kanaya
Shigenori
S
D000596:Amino Acids / Q000737:chemistry*; D019843:Archaeal Proteins / Q000737:chemistry* / Q000235:genetics; D002942:Circular Dichroism; D004795:Enzyme Stability; D019791:Guanidine / Q000737:chemistry; D006358:Hot Temperature; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D011487:Protein Conformation; D017510:Protein Folding; D016914:Ribonuclease H / Q000737:chemistry* / Q000235:genetics; D019712:Thermococcus / Q000201:enzymology*
D000596:Amino Acids; D019843:Archaeal Proteins; C091139:ribonuclease HII; D016914:Ribonuclease H; D019791:Guanidine