A protein kinase chaperone complex required for the proper folding, maturation and stabilization of target proteins (mostly signalling protein kinases, some steroid hormone receptors), usually during or immediately after completion of translation. The highly conserved, phosphorylated CDC37-Ser13 is essential for complex assembly and target protein binding. CDC37-Ser13 is phosphorylated by Casein kinase II (CK2), which in turn is a target of CDC37 creating a positive feedback loop. CDC37-Ser13 is de-phosphorylated by PP5 (P53041). Target proteins are recognised by the CDC37 subunit. HSP90 does not bind any particular motif but rather associates with intrinsically unstable kinases. Complex binding also prevents rapid ubiquitin-dependent proteosomal degradation of target proteins.