The 70 kD heat shock cognate protein, Hsc70 is closely related biochemically and biologically to Hsp70 and is part of the Hsp70 family which contains a number of highly-related protein isoforms ranging in size from 66kD to 78kD. These proteins include both cognate members which are found within major intracellular compartments and highly inducible isoforms which appear to be predominantly cytoplasmic or nuclear in distribution (1). Members of the Hsp70 family are molecular chaperones which are involved in many cellular functions such as protein folding, transport, maturation and degradation and they exert their function in an ATP-dependent manner. The molecular chaperones of the Hsp70 family recognize and bind to nascent polypeptide chains as well as partially folded intermediates of proteins preventing their aggregation and misfolding and the binding of ATP triggers a critical conformational change leading to the release of the bound substrate protein (2). Recent data has demonstrated that BAG-1 which possesses a ubiquitin-like domain at its amino terminus modulates the chaperone activity of Hsc70 and Hsp70. These findings reveal a role of BAG-1 as a physical link between the Hsc70/Hsp70 chaperone system and the proteasome (3). There is also experimental data which shows that the ATPase domain and the substrate binding domain of Hsc70 cooperate and form a cochaperone-chaperone complex with the synaptic vesicle cysteine string protein (csp) which is essential for normal neurotransmitter release (4).
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