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• For protein expression, HEK293F cells cultured in Free Style 293 medium at a density of 2.5×106 cells per ml were infected with 10% volume of P2 virus.
• OX2-p22 complex was mixed with MSP2X and L-α-phosphatidylcholine from soybean (PC, Type II-S, 14–23% choline basis, Sigma P5638, solubilized in 68.49 mM octyl glucoside) at a molar ratio of protein: MSP2X: PC = 1:4:800.
• The supernatant containing NOX2-p22 complex reconstituted in lipid nanodisc was loaded onto the 1 ml Streptactin Beads 4FF column to remove empty nanodisc.
• Sodium butyrate (10 mM) and 5-aminolevulinic acid hydrochloride (200 μM) was added to the culture 12 hr after transfection to promote haem incorporation, and the cells were transferred to a 30°C incubator for another 36 hr before harvesting.
• For purification, cell pellets were resuspended in Buffer A (20 mM HEPES pH 7.5, 150 mM NaCl, 2 μg/ml aprotinin, 2 μg/ml pepstatin, 2 μg/ml leupeptin, 20% (v/v) glycerol, 1 mM DTT) containing 1 mM phenylmethanesulfonyl fluoride, 2 mM EGTA, 10 mM MgCl2, 10 μg/ml DNAse, 19.6 mM dodecylmaltoside (DDM), and 1.65 mM cholesteryl hemisuccinate.

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