hsc 70

HSPA8, also known as HSC70, is a member of the heat shock protein family due to homology with other heat shock proteins. The heat shock protein 70 family is comprised of both heat-inducible and constitutively expressed members. The latter are called heat-shock cognate proteins. HSPA8 belongs to the heat-shock cognate subgroup. Members of the human heat-shock protein multigene family have several highly conserved proteins with structural and functional properties in common but vary in the extent of their inducibility in response to metabolic stress. HSPA8 is constitutively expressed and performs functions related to normal cellular processes. This protein binds to nascent polypeptides to facilitate correct protein folding. It also functions as an ATPase in the disassembly of clathrin-coated vesicles during the transport of membrane components through the cell. Two alternatively spliced variants have been characterized to date. HSPA8 acts as a repressor of transcriptional activation. It inhibits the transcriptional coactivator activity of CITED1 on Smad-mediated transcription. Isoform 2 may function as an endogenous inhibitory regulator of HSC70 by competing with the co-chaperones. It also is an ATPase that works with Auxilin to remove clathrin-coated vesicles. In neurons, synaptojanin is also an important protein involved in vesicle uncoating.

BAG Family Molecular Chaperone Regulator 2 (BAG2) is a member of the Bag family whose members compete with Hip for binding to the Hsc70/Hsp70 ATPase domain and promote substrate release. BAG2 contains 1 BAG domain and is a important component of the HSC 70/CHIP chaperone-dependent ubiquitin ligase complex. In mammalian cells BAG1, BAG2, and BAG3 bind with high affinity to the ATPase domain of Hsc70 and inhibit its chaperone activity in a Hip-repressible manner.