Effect of free and ATP-bound magnesium and manganese ions on the ATPase activity of chaperonin GroEL14.
Hydrolysis of ATP by the GroEL14 chaperonin oligomer is activated and modulated by Mg2+ or Mn2+ ions. Mg-ATP and Mn-ATP can serve as substrates of the reaction and bind in a positively cooperative manner to the same catalytic sites on GroEL14, with similar binding constants in the micromolar range. In addition, millimolar amounts of Mg2+ and Mn2+ ions can further activate the GroEL14-ATPase while interacting with low-affinity noncatalytic sites on the chaperonin. The extent of ATPase activation by Mn2+ is half of that by Mg2+ ions. When both Mg2+ and Mn2+ ions are present in the same reaction, Mn2+ behaves as a noncompetitive partial inhibitor of the Mg-dependent ATPase. This inhibition requires the presence of ADP in the catalytic site. The binding affinity of Mn-ADP to the site is significantly higher than that of Mg-ADP. A slower release of Mn-ADP from the catalytic site thus changes the rate-determining step of the GroEL14-ATPase cycle. In the cell, the concentrations of Mg2+ and Mn2+ ions are such that both divalent ions may modulate chaperonin activity.
Diamant
S
S
Department of Botany, Alexander Silberman Institute of Life Sciences, Hebrew University of Jerusalem, Israel.
Azem
A
A
Weiss
C
C
Goloubinoff
P
P
D000251:Adenosine Triphosphatases / Q000187:drug effects / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D001665:Binding Sites; D017301:Ca(2+) Mg(2+)-ATPase / Q000037:antagonists & inhibitors; D018834:Chaperonin 60 / Q000187:drug effects / Q000378:metabolism*; D004789:Enzyme Activation; D006868:Hydrolysis; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism / Q000494:pharmacology*; D008345:Manganese / Q000378:metabolism / Q000494:pharmacology*
D018834:Chaperonin 60; D008345:Manganese; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D017301:Ca(2+) Mg(2+)-ATPase; D008274:Magnesium