Final answer:
Calnexin is the only known protein quality control factor that operates as a protease without the dependence on ATP, unlike Ubiquitin and Proteasome systems.
Step-by-step explanation:
The only known protein quality control factor that isn't ATP-dependent is Calnexin, which is a protease. While the proteasome complex, which includes ubiquitin-proteasomal degradation pathway, is indeed involved in protein degradation and depends on ATP for its function, Calnexin operates independently of ATP. Calnexin is responsible for ensuring the proper folding of newly synthesized proteins and does not require ATP to function, unlike the proteasome and ubiquitin system, which tag defective or unneeded proteins for degradation in an ATP-dependent manner.