Inhibits the chaperone activity of HSP70/HSC70 by promoting substrate release. Has anti-apoptotic activity.
Defects in BAG3 are the cause of myopathy myofibrillar BAG3-related (MFM-BAG3) [MIM:612954]. A neuromuscular disorder that results in early-onset, severe, progressive, diffuse muscle weakness associated with cardiomyopathy, severe respiratory insufficiency during adolescence, and a rigid spine in some patients. At ultrastructural level, muscle fibers display structural alterations consisting of replacement of the normal myofibrillar markings by small, dense granules, or larger hyaline masses, or amorphous material.