The cells were pre-treated with lysozyme (0.7 mg ml−1 final concentration) and incubated at 37 °C for 30 min. DNase I was added to the cells prior to lysis and the pressing was conducted at a cell pressure of 2.9 MPa in an Aminco French pressure cell. The pressing was repeated for maximum lysis. The lysate was loaded onto a 15 %/40 % (wt/wt) sucrose step gradient and centrifuged in a Beckman Ti 45 rotor for 10 h at 57,000×g at 4 °C. The intracytoplasmic membrane fraction was harvested from the interface BIBW2992 concentration and further treated to concentrate the membranes by diluting out the sucrose with 10 mM HEPES pH 7.4 buffer and centrifuging in a Beckman

Ti 45 rotor for 2 h at 125,000×g at 4 °C. The membrane pellet was re-suspended in a small volume, typically 1 ml of 10 mM HEPES pH 7.4 buffer, and frozen at −20 °C for further use. The membrane pellet obtained from sucrose gradient centrifugation were solubilised with n-dodecyl-beta-D-maltoside (β-DDM, Glycon) at a final concentration of 59 mM, and a final OD of the membrane sample of ~60 at 875 nm. The mixture was stirred at 4 °C in the dark for 90 min. Non-solubilised CFTRinh-172 material was removed by centrifugation (in a Beckman Ti 45 rotor for 2 h at 125,000×g), and the supernatant was loaded onto Chelating Sepharose

Fast Flow Ni–NTA column (GE Healthcare) equilibrated with 10 mM HEPES pH 7.4, 500 mM NaCl, 10 mM Imidazole, 0.59 mM β-DDM buffer. A gradient of 10–400 mM imidazole was applied and the main peak, which contains pure His12-RC-LH1-PufX, Idasanutlin mouse appeared when the concentration of imidazole reached ~300 mM. Eluted protein was concentrated (Vivaspin 500 spin-concentrator, Sartorius) and dialyzed against 10 mM HEPES pH 7.4, 50 mM NaCl, 0.59 mM β-DDM buffer. Then, the RC-His12-LH1-PufX protein was loaded onto a DEAE-Sepharose (Sigma) ion-exchange column equilibrated with 10 mM HEPES Cepharanthine pH 7.4, 50 mM NaCl, 0.59 mM β-DDM buffer. A gradient of 50–300 mM NaCl was applied with the main peak of pure protein appearing at NaCl concentration of ~280 mM. The best fractions

judged from the peak absorbance ratio of 875–280 nm were pooled (A 880/A 280 ~ 1.9). The protein was again concentrated and dialyzed against 10 mM HEPES pH 7.4, 50 mM NaCl, 0.59 mM β-DDM buffer and applied to a HPLC column (Phenomenex BioSep) and eluted at a flow rate of 0.3 ml min−1 in order to separate the monomeric and dimeric RC-His12-LH1-PufX complexes. The second elution peak (corresponding to the monomeric fraction of RC-His12-LH1-PufX) was collected, concentrated to a final concentration of 15 μM in 10 mM HEPES pH 7.4, 50 mM NaCl, 0.59 mM β-DDM buffer and stored at −80 °C for further use. Cyt c 2-His6 The gene encoding cyt c 2 was amplified from genomic DNA from Rba. sphaeroides 2.4.