The molecular chaperone Hsp90, a dimeric ATP-driven molecular machine, is one of the most abundant proteins found in eukaryotic cells. This specialised chaperone is known to function as part of several complexes to assist in several essential cellular functions including the folding, maintenance and degradation of client proteins, although the exact mechanisms by which these functions occur is not yet known. In order to elucidate the function of this crucial molecule, the mechanisms and roles of the large conformational changes it undergoes and the forces involved must be studied. To achieve this, experimental techniques will be used that provide excellent force sensitivity and high spatial resolution. In combination with in vivo experiments, I will use custom-built optical trapping and fluorescence setups together with biochemical approaches and mutagenesis, which will provide me with a unique set of tools with which to delineate the specific domain orientations and forces that are required for the function of Hsp90. This will enable me to address the timely question of how the conformations and mechanics of Hsp90 are influenced by co-chaperones and client proteins.