HSP90 proteins are highly conserved molecular chaperones that have key roles in signal transduction, protein folding, protein degradation, and morphologic evolution. HSP90 proteins normally associate with other cochaperones and play important roles in folding newly synthesized proteins or stabilizing and refolding denatured proteins after stress. TRAP1 is a mitochondrial HSP90 protein. Other HSP90 proteins are found in cytosol (see HSP90AA1; MIM 140571) and endoplasmic reticulum (HSP90B1; MIM 191175) (Chen et al., 2005 [PubMed 16269234]).