ATPase cycle of an archaeal chaperonin.
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.
Gutsche
I
I
Max-Planck-Institute for Biochemistry, Am Klopferspitz 18a, Martinsried, D-82152, Germany. gutsche@biochem.mpg.de
Mihalache
O
O
Baumeister
W
W
D000244:Adenosine Diphosphate / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000494:Allosteric Regulation; D000495:Allosteric Site; D019843:Archaeal Proteins; D002384:Catalysis; D018833:Chaperonins / Q000737:chemistry / Q000378:metabolism*; D005453:Fluorescence; D006868:Hydrolysis; D007536:Isomerism; D007700:Kinetics; D010710:Phosphates / Q000378:metabolism; D011485:Protein Binding; D013816:Thermodynamics; D013822:Thermoplasma / Q000201:enzymology*; D056405:Thermosomes; D017186:Titrimetry; D014462:Ultrafiltration
D019843:Archaeal Proteins; D010710:Phosphates; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D018833:Chaperonins; D056405:Thermosomes