Highly effective methods for expression/purification of recombinant human HSP90 and its four distinct (N-LR-M-C)...

Heat shock protein 90 (HSP90) plays essential roles in the normal physiology and comprises four distinct domains, including NH₂-terminal (N), charged linker region (LR), middle (M), and COOH-terminal (C) domains, all of which regulate HSP90 biological functions. We reported herein detailed protocols to produce recombinant full-length (FL) and all these four domains of human HSP90 from Escherichia coli. cDNAs encoding FL, N, LR, M and C domains of human HSP90α were amplified and cloned into pET-32b(+) expression vector. All HSP90 constructs were expressed as soluble Trx-His-S tagged proteins after induction with 0.25 mM isopropyl-β-d-thiogalactopyranoside (IPTG) at 18 °C overnight and further purified by affinity chromatography using nickel-nitrilotriacetic acid (Ni-NTA) resin. The enterokinase (EK) digestion was optimized for efficient cleavage of the Trx-His-S tag from each HSP90 construct by varying concentrations of EK (0.5-1 U) and urea (0-3 M). Each HSP90 construct was highly purified and approximately 0.1-1 mg proteins were obtained from 100 ml of bacterial culture. All the purified HSP90 constructs were successfully confirmed by tandem mass spectrometry (nanoLC-ESI-ETD MS/MS) and their secondary structure was quantified using attenuated total reflection - Fourier-transform infrared (ATR-FTIR) spectroscopy. Our expression and purification protocols would facilitate further structural and functional studies of human HSP90.