The diverse roles of J-proteins, the obligate Hsp70 co-chaperone.

Hsp70s and J-proteins, which constitute one of the most ubiquitous types of molecular chaperone machineries, function in a wide variety of cellular processes. J-proteins play a central role by stimulating an Hsp70's ATPase activity, thereby stabilizing its interaction with client proteins. However, while all J-proteins serve this core purpose, individual proteins are both structurally and functionally diverse. Some, but not all, J-proteins interact with client polypeptides themselves, facilitating their binding to an Hsp70. Some J-proteins have many client proteins, others only one. Certain J-proteins, while not others, are tethered to particular locations within a cellular compartment, thus "recruiting" Hsp70s to the vicinity of their clients. Here we review recent work on the diverse family of J-proteins, outlining emerging themes concerning their function.