Fig. 2.
Cryo-EM structure of the YaxAB complex reveals an α-helical transmembrane pore. a Negative-stain TEM micrographs of YaxAB complexes in solution. Left: sample in absence of detergent. Right: sample in presence of 0.1% Cymal-6. Scale bar = 50 nm. b Final sharpened cryo-EM density of YaxAB together with the fitted pore model, shown from side view. The chosen contour level (4.5σ) corresponds to the 1.21 Å3/Dalton convention according to Harpaz et al.65. Fitted YaxA and YaxB models are colored blue and pink, respectively. The amphipol belt, illustrated in gold, is clearly visible and demarcates the putative transmembrane region. c Top view of the pore complex, overlaid with the final cryo-EM map. YaxA and YaxB form outer and inner rings, respectively (left). A zoom of the amphipol-enclosed portion of the complex (right) is contoured at 6.5σ to better distinguish individual helices. Labels of the secondary structure elements adhere to the nomenclature shown in Fig. 1b. d Pore diameter plotted against the coordinate along the vertical axis. Calculations have been performed using the program HOLE66 (left). The red line indicates the narrowest point in the channel. Two major constrictions along the YaxAB model are emphasized (right)