Assembly of the 26 S complex that degrades proteins ligated to ubiquitin is accompanied by the formation of ATPase activity.
In the ubiquitin pathway for intracellular protein breakdown, proteins ligated to ubiquitin are degraded by a large (26 S) ATP-dependent protease complex. It was found previously that the 26 S complex is assembled from three different enzyme components by a process that requires MgATP. In addition, MgATP is also required for the continued action of the 26 S complex in the breakdown of ubiquitin-protein conjugates. In the present study we have tried to gain some insight into the mode of action of ATP by following ATP hydrolysis by the 26 S complex and its three components. It was found that none of the three unassembled components had significant ATPase activity, but such activity appeared following their entry into the 26 S complex. The presence of all three components and of MgATP was required for the formation of complex-associated ATPase activity. GTP and UTP cannot replace ATP for complex assembly, but these nucleotides can substitute for ATP in the stimulation of the conjugate-degrading activity of the 26 S complex. Unlabeled GTP and UTP inhibit the hydrolysis of [gamma-32P] ATP by complex-associated ATPase, indicating that this activity is related to the latter site of ATP action in this system.
Armon
T
T
Unit of Biochemistry, Faculty of Medicine, Technion-Israel Institute of Technology, Haifa.
Ganoth
D
D
Hershko
A
A
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D010450:Endopeptidases / Q000378:metabolism*; D007700:Kinetics; D009097:Multienzyme Complexes / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D011485:Protein Binding; D011817:Rabbits; D012156:Reticulocytes / Q000378:metabolism; D012265:Ribonucleotides / Q000378:metabolism; D014452:Ubiquitins / Q000378:metabolism*
D009097:Multienzyme Complexes; D012265:Ribonucleotides; D014452:Ubiquitins; D000255:Adenosine Triphosphate; D010450:Endopeptidases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D000251:Adenosine Triphosphatases