The gene was cloned using Touchdown PCR and sub-cloned into the pRK415 vector using EcoRI and HindIII restriction sites GS-1101 for directional cloning. The plasmid with the gene was then mated into a ΔcycA strain of Rhodobacter sphaeroides via Escherichia coli S17 (Simon et al. 1983). The intracytoplasmic membrane fraction from the cyt c 2-His6 mutant was prepared in exactly the same way as described in the paragraph above. The membrane pellet obtained from sucrose gradient centrifugation

was solubilised with N,N-dimethyldodecan-1-amine oxide (LDAO, Fluka) at a final concentration of 65 mM, and a final OD of the membrane sample of ~80 at 875 nm. The NSC 683864 datasheet mixture was stirred at room temperature in the dark for 20 min. Non-solubilised 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, 1 mM LDAO buffer. A gradient of 10–400 mM imidazole was applied and the purified cyt selleck compound c 2-His6 eluted when the concentration of imidazole reached ~270 mM. The purified protein (A 414/A 280

ratio ≥3.3) was dialyzed against 10 mM HEPES pH 7.4, 50 mM NaCl, 1 mM LDAO buffer, concentrated to a final concentration of 740 μM and stored at −80 °C for further use. AFM probes and sample substrates functionalization Epitaxially grown Au [111] thin layers (PHASIS, Switzerland) were functionalised, as received and without further treatment, with mixed EG3/Ni–NTA thiol self-assembled monolayer. Hybrid AFM probes, Si tips mounted on Si3N4 IMP dehydrogenase triangular cantilevers, model SNL or MSNL (Bruker), were

first cleaned by washing in acetone (HPLC grade, Fisher Scientific) and then cleaned in a home-built UV/Ozone cleaner (LSP035 Pen-Raylight source, LOT-Oriel Ltd.) for 45 min. Immediately after the cleaning step the AFM probes were placed into a thermal evaporator (Auto 306, Edwards, UK) and were coated first with ~4 nm of adhesive chromium layer, followed by ~30 nm of gold layer on the tip side. After that the AFM probes were functionalised with mixed EG3/Ni–NTA thiol SAM. Briefly, both the gold substrates and the AFM probes were immersed in an ethanolic solution of EG3-thiol ((11-Mercaptoundecyl)tri(ethylene glycol), Sigma-Aldrich) and Ni–NTA-thiol (HS-C11EG3-NTA from ProChimia Surfaces Sp. z o.o., Poland) mixed at a ratio of either 1:200 (mol/mol)—when used for substrate functionalization—or 1:5 (mol/mol) when used to functionalised AFM probes with a final total concentration of thiols of 1 mM. The functionalization was carried out for 16 h with subsequent wash in pure HPLC grade ethanol (Sigma-Aldrich). In the next step, the NTA end-groups of the monolayer were charged with Ni2+ ions by incubation in 70 mM aqueous solution of NiSO4 with subsequent washing of the substrates and the AFM probes in pure water.