Differential disruption of Munc18-1 binding to the SNARE complex by Munc18-1 point mutations. (A) Sample traces of the methyl regions of 1D ¹³C-edited ¹H-NMR spectra of 2 µM SNARE complex containing uniformly ¹³C-labeled syntaxin-1(2–243) in the absence or presence of 2.5 µM of unlabeled WT or mutant Munc18-1s. ppm, parts per million. (B) Binding curves obtained from the SMR intensities observed in 1D ¹³C-edited ¹H-NMR spectra of 2 µM SNARE complex containing uniformly ¹³C-labeled syntaxin-1(2–243) in the presence of increasing amounts of unlabeled WT or mutant Munc18-1s. The data were fit to a standard single-site binding model and normalized to the percentage of binding using as limit values the initial intensity in the absence of Munc18-1 (0% binding) and the intensity extrapolated to infinite Munc18-1 concentration (100% binding).