HSP90 - Middle Domain

The middle domain on Hsp90 is implicated in binding to the client protein – for example, PKB. Shown below is the amphipathic loop (residue 329-339) implicated in binding to the client protein.

The loop is present on both protomers of the dimer, but due to high disorder only one is shown in the crystal structure.
The conformation change in the N-terminal on ATP binding brings the middle terminals closer together, acting as a clamp on the client protein. This clamping allows Hsp90 to assist in folding and prevention of protein aggregation, as well as facilitating transport.

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