Detailed protocol for optimised expression and purification of functional monomeric human Heat Shock Factor 1

Heat Shock Factor 1 (HSF1) is the master regulator of the heat shock response, a universal survival mechanism throughout eukaryotic species used to buffer potentially lethal proteotoxic conditions. HSF1's function in vivo is regulated by several factors, including post translational modifications and elevated temperatures, whereupon it forms trimers to bind with heat shock elements in DNA. Unsurprisingly, HSF1 is also extremely sensitive to elevated temperatures in vitro, which poses specific technical challenges when producing HSF1 using a recombinant expression system. Although there are several useful publications which outline steps taken for HSF1 expression and purification, studies that describe specific strategies and detailed protocols to overcome HSF1 trimerisation and degradation are currently lacking. Herein, we have reported our detailed experimental protocol for the expression and purification of monomeric human HSF1 (HsHSF1) as a major species. We also propose a refined method of inducing HsHSF1 activation in vitro, that we consider more accurately mimics HsHSF1 activation in vivo and is therefore more physiologically relevant.