Figure 3.

(a) The interactions observed in the native membrane are highlighted on the corresponding structures. (b–g) PELDOR data for TonB_ΔTMD dimers or BtuB–TonB_ΔTMD binding using NO, Gd³⁺, or OX063 trityl labels as indicated in the native membranes. (b, c) 36 μM TonB_ΔTMD was added to 18 μM BtuB, (d–g) 20 μM TonB_ΔTMD was added to 20 μM BtuB, or (h) 20 μM BtuB was mixed with 20 μM (4-pulse PELDOR) or 10 μM (5-pulse PELDOR) T-CNCbl. For P(r), distances obtained from Tikhonov regularization (TR) using DeerAnalysis⁴⁴ and DEERNet⁴⁵ are overlaid. The DeerLab⁴⁶ analysis gave nearly identical outputs (Figure S5). For (c), the form factor corresponding to a single Gaussian fit (5.9 ± 0.4 nm, dotted pink line, see Figure S3) or (h) a two Gaussian fit (5.6 ± 0.4 and 6.8 ± 0.4 nm, pink line), respectively, is shown. In (h), the 4-pulse and 5-pulse PELDOR data were globally analyzed using the DeerLab software package. For the nonidentical spin pairs, the pump (p) and observer (obs) spins are indicated. Corresponding simulations (b and c using PDB 1IHR, d–g using PDB 2GSK, and h using PDB 1NQH) are overlaid (in gray dotted lines).