Hsp90 is a molecular chaperone and is one of the most abundant proteins in unstressed cells. In mammalian cells, there are two genes encoding cytosolic Hsp90 homologues, with the human Hsp90α showing 85% sequence identity to Hsp90β. The recombinant Hsp90 produced from Sf9 cells represents the full length (a.a. 1-723) of Hsp90b subunit.