BAG proteins compete with Hip-1 for binding to the Hsc70/Hsp70ATPase domain and promote substrate release. All the BAG proteins have an approximately 45-amino acid BAG domain near the C terminus but differ markedly in their N-terminal regions. The protein encoded by this gene contains a WW domain in the N-terminal region and a BAG domain in the C-terminal region. The BAG domains of BAG1, BAG2, and BAG3 interact specifically with the Hsc70 ATPase domain in vitro and in mammalian cells. All 3 proteins bind with high affinity to the ATPase domain of Hsc70 and inhibit its chaperone activity in a Hip-repressible manner.[7]
BAG gene has been implicated in age related neurodegenerative diseases such as Alzheimer's. It has been demonstrated that BAG1 and BAG3 regulate the proteasomal and lysosomal protein elimination pathways, respectively.[10][11] It has also been shown to be a cause of familial dilated cardiomyopathy.[12]
That BAG3 mutations are responsible for familial dilated cardiomyopathy is confirmed by another study describing 6 new molecular variants (2 missense and 4 premature Stops
). Moreover, the same publication reported that BAG3 polymorphisms are also associated with sporadic forms of the disease together with HSPB7 locus.[13]
In muscle cells, BAG3 cooperates with the molecular chaperones Hsc70 and HspB8 to induce the degradation of mechanically damaged cytoskeleton components in lysosomes. This process is called chaperone-assisted selective autophagy and is essential for maintaining muscle activity in flies, mice and men.[8]
BAG3 is able to stimulate the expression of cytoskeleton proteins in response to mechanical tension by activating the transcription regulators YAP1 and WWTR1.[9] BAG3 balances protein synthesis and protein degradation under mechanical stress.
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