Gutsche I, Mihalache O, Baumeister W
Max-Planck-Institute for Biochemistry, Am Klopferspitz 18a, Martinsried, D-82152, Germany.
J Mol Biol. 2000 Jun 30;300(1):187-96. doi: 10.1006/jmbi.2000.3833.
Recent structural data imply differences in allosteric behavior of the group I chaperonins, typified by GroEL from Escherichia coli, and the group II chaperonins, which comprise archaeal thermosome and eukaryotic TRiC/CCT. Therefore, this study addresses the mechanism of interaction of adenine nucleotides with recombinant alpha-only and native alphabeta-thermosomes from Thermoplasma acidophilum, which also enables us to analyze the role of the heterooligomeric composition of the natural thermosome. Although all subunits of the alpha-only thermosome seem to bind nucleotides tightly and independently, the native chaperonin has two different classes of ATP-binding sites. Furthermore, for the alpha-only thermosome, the steady-state ATPase rate is determined by the cleavage reaction itself, whereas, for the alphabeta-thermosome, the rate-limiting step is associated with a post-hydrolysis isomerisation into a non-covalent ADP*P(i) species prior to the release of the gamma-phosphate group. After half-saturation with ATP, a negative cooperativity in hydrolysis is observed for both thermosomes. The effect of Mg(2+) and K(+) nucleotide cycling is documented. We conclude that archaeal chaperonins have unique allosteric properties and discuss them in the light of the mechanism established for the group I chaperonins.
最近的结构数据表明，以大肠杆菌的GroEL为代表的I型伴侣蛋白和包括古菌热体和真核生物TRiC/CCT的II型伴侣蛋白在变构行为上存在差异。因此，本研究探讨了嗜热栖热菌重组的仅α亚基热体和天然αβ热体与腺嘌呤核苷酸的相互作用机制，这也使我们能够分析天然热体异源寡聚体组成的作用。尽管仅α亚基热体的所有亚基似乎都能紧密且独立地结合核苷酸，但天然伴侣蛋白有两类不同的ATP结合位点。此外，对于仅α亚基热体，稳态ATP酶速率由裂解反应本身决定，而对于αβ热体，限速步骤与在γ-磷酸基团释放之前水解后异构化为非共价ADP*P(i)物种有关。用ATP半饱和后，观察到两种热体在水解方面都存在负协同效应。记录了Mg(2+)和K(+)核苷酸循环的影响。我们得出结论，古菌伴侣蛋白具有独特的变构特性，并根据为I型伴侣蛋白建立的机制对其进行了讨论。
