FKBP Co-Chaperones in Steroid Receptor Complexes

Molecular chaperones are critical for cell survival by assuring proper protein folding in general, but chaperones, in particular the Hsp90 machinery, are also important for the activity of multiple specific client proteins involved in cellular signal transduction pathways. One class of extensively studied Hsp90 client is the steroid receptor subfamily of nuclear receptors. Chaperones are required for folding and stabilizing steroid receptors in a functionally competent state for hormone binding, and chaperones can also modulate steroid receptor responsiveness to hormone binding. In this chapter, we review recent advances in understanding the biochemical and physiological functions of a class of co-chaperones, the Hsp90-binding peptidylprolyl isomerases, that populate steroid receptor complexes.