8.A.163.1.1
HSP90AB1 (HSP90B, HSPC2, HSPCB) of 724 aas, which forms a complex with the cochaparone protein, CDC37 (378 aas) and AHA1 (338 aas), in the cytoplasm.  HSP90 is an ATP-driven chaparone. It promotes the maturation, structural maintenance and proper regulation of specific target proteins including integral membrane proteins and transporters involved, for instance, in cell cycle control, signal transduction and transport. It undergoes a functional cycle linked to its ATPase activity. This cycle probably induces conformational changes in the client proteins, thereby causing their activation. It also interacts dynamically with various co-chaperones that modulate its substrate recognition, ATPase cycle and chaperone function (Chadli et al. 2006, Retzlaff et al. 2009). In the resting state, through the dimerization of its C-terminal domain, HSP90 forms a homodimer which is defined as the open conformation. Upon ATP-binding, the N-terminal domain undergoes significant conformational changes and comes in contact to form an active closed conformation. After HSP90 finishes its chaperoning tasks of assisting the proper folding, stabilization and activation of client proteins under the active state, ATP molecule is hydrolyzed to ADP which then dissociates from HSP90 and directs the protein back to the resting state (Richter et al. 2008). The chaparone complex interacts with cereblon (CDBN; TC# 8.A.162.1.1) which determines HSP90 activity toward transmembrane proteins (Heider et al. 2021).