Figure 5. CD spectra of purified TorA^His, TorD^His, and the TorA–TorD^His and TorA_ΔSP–TorD^His complexes.

CD spectra (185–260 nm) were collected in quartz cells of 0.02 cm pathlength at 25°C with a scan speed of 10 nm/min, bandwidth of 1 nm, response of 2 s and data pitch of 0.2 nm. The buffer used was 50 mM Tris/H₂SO₄ (pH 7.5), 200 mM K₂SO₄ and 1 mM DTT, and protein concentrations were: TorA, 0.7 mg/ml; TorD, 1 mg/ml; TorA–TorD^His, 1 mg/ml; and TorA_Δsp–TorD^His, 0.5 mg/ml.