Interspin distance distributions detected with nitroxide-labeled periplasmic Cys pair 164/310 ((a) in absence of a binding sugar and (b) in presence of a binding sugar) and cytoplasmic Cys pair 73/340 ((c) in absence of a binding sugar and (d) in presence of a binding sugar). The top panel shows the respective conformations to which the interspin distances are attributed: blue: outward-facing; gray: occluded intermediate; orange: apo intermediate; and green: inward-facing; the yellow stars indicate the position of the label on LacY relative to the membrane. Distance distributions obtained by Tikhonov regularization of dipolar spectra are shown (solid blue line with no bound sugar; solid red line with bound sugar). Relative distributions of conformational populations are obtained by multi-Gaussian deconvolution. Peak centers, indicated on top of the Gaussian peaks, represent the distance between the nitroxides at these positions (interspin distance). The relative area of the respective Gaussian peaks is indicated (%) and represents the fraction of each conformational population in the multi-Gaussian fit (broken black line). The figure is adapted from [39].