Fig 2: Related to Figure 2. The conservation of the primary interface.a, Primary sequence alignments between neuronal and airway systems (Stx1A vs. Stx3, SNAP-25A vs. SNAP-23, and Syt1 vs. Syt2). White: absolutely conserved, grey: similar, black: not conserved. Red boxes indicate residues involved in salt bridges and hydrogen bonds, orange boxes indicate residues involved in hydrophobic interactions in the primary interface. The yellow line indicates the residues of SP9 shown as the yellow region in panel b and c. b, Close-up view of the primary interface (PDB ID 5W5C) with grey colour and labels indicating the locations of sequence differences in the primary interface between the neuronal and airway epithelial systems (SNAP-25A vs. SNAP-23, Syt1 vs. Syt2); the corresponding labels indicate the sequence differences. Yellow: region that corresponds to SP9 with staples shown as dumbbells. c, Close-up view of the primary interface with residues shown as sticks that are important for the primary interface, including R281, E295, Y338, R398, R399 in Syt1 C2B (also corresponding to residues mutated in Syt1(QM)) and K40, D51, E52, E55, Q56, D166 in SNAP-25A and D231, E234, E238 in Stx1A. Yellow: region that corresponds to SP9 with staples shown as dumbbells.d, Starting point of the molecular dynamics simulations of the primary interface. e, End points of five independent 1-µsec simulations (colours) of the primary interface. f, Starting point of the SP9–Syt1-C2B simulations. g, Starting point of the P9–Syt1-C2B simulations. All starting points were derived from the crystal structure with PDB ID 5W5C.

Fig 3: Mucin secretion defects in Syt2-mutant mice.a, Transverse sections of bronchial airways of mice stained with periodic acid fluorescent Schiff (PAFS) to demonstrate mucin with red fluorescence. Top, in naive mice without airway inflammation, scant intracellular mucin is visible. Treatment with IL-13 increases mucin synthesis, resulting in abundant intracellular mucin. Bottom, subsequent treatment with ATP induces mucin secretion, reducing intracellular mucin in WT C57Bl/6J mice (WT) and Syt2F/F mice (F/F), but not in Syt2D/D mice (D/D). Scale bar, 50 µm. b, Fractional mucin secretion was measured by analysing images of airways of mice treated with IL-13 alone and comparing those with those of mice treated with IL-13 followed by ATP, as shown in a. Individual data points and box plots are shown for two independent sets of experiments combined to give a total n mice (indicated below each box plot) per group (Supplementary Table 1). Comparison with the Syt2F/F group of mice was performed using two-tailed unpaired Student’s t-tests; ***P = 0.00026. c, Transverse sections of bronchial airways of mice treated with IL-13, then with methacholine (Mch) to induce smooth muscle contraction and mucin secretion, and fixed with methacarn and stained with PAFS to demonstrate lumenal mucus and residual intracellular mucin. Scale bar, 50 µm. d, The sum of the lumenal mucus cross-sectional area in the left lung measured at 500 µm intervals. Individual data points and box plots are shown for two independent sets of experiments combined to give a total of n mice (indicated below each box plot) per group (Supplementary Table 1). Comparison with the Syt2F/F group of mice was performed using two-tailed unpaired Student’s t-tests; **P = 0.0012.Source data

Fig 4: Related to Figure 1. Efficiency of Syt2 deletion in airway secretory cells.Bronchial airways of Syt2WT and Syt2D/D mice were stained with antibodies to Syt2 and secondary antibodies conjugated to horseradish peroxidase (brown colour, see Methods). Secretory cells in Syt2 WT mice (left panel) have a domed appearance with their apical poles staining intensely for Syt2 (filled triangle). There was less intense linear staining of tufted ciliated cells in the region of ciliary basal bodies (open triangle), which often stain non-specifically. Secretory cells in Syt2D/D mice did not stain for Syt2 (filled triangle), but linear staining of ciliated cells was similar to that in Syt2WT. We enumerated secretory cells in 3 mice of each genotype and found 46% in Syt2WT and 48% in Syt2D/D, ±4%, which did not differ significantly, indicating there was no loss of viability of secretory cells in Syt2D/D mice. In Syt2WT mice, 91% of secretory cells stained for Syt2, whereas in Syt2D/D mice, only 7% stained for Syt2, indicating a deletion efficiency ~92%. Results for Syt2F/F mice were indistinguishable from those for Syt2WT. Scale bar, 50 µm. Experiments were repeated twice with similar results.

Fig 5: Characterization of SP9.a, Magnified view of the primary interface between the neuronal SNARE complex (VAMP-2 (blue), Stx1 (red) and SNAP-25A (green)) and the C2B domain of Syt1 (orange) (Protein Data Bank (PDB): 5W5C), indicating the region (yellow) that corresponds to the stapled peptide SP9 with staples shown as dumbbells. b, Schematic of the synthesis of SP9. Hydrocarbon-stapled peptides are formed by cross-linking residues at the specified positions. c, Sequences of peptides. S5 indicates S stereochemistry at the a-carbon, with 5 carbon atoms in the olefinic side chains. The superscripts denote the start and end positions of the SNAP-25A sequence. d, Circular dichroism (CD) spectra of 100 mM peptides measured at pH 7.4 and at 25 ± 1 °C. e, The percentage of a-helical content in these peptides was estimated by dividing the mean residue ellipticity [f]222obs by the reported [f]222obs for a model helical decapeptide. f, Interactions between Cy3-labelled SP9 or P0 and unlabelled Syt1 C2B, the quintuple Syt1 C2B(QM) mutant and Syt2 C2B as measured by bulk fluorescence anisotropy (Methods). Data are mean ± s.e.m. along with individual data points from n = 3–7 independent experiments. Hill equations were fit to estimate the dissociation constant Kd, where the Hill coefficients were constrained to 1. g, Peptide conformations (colours) after five independent 1 µs molecular dynamics simulations of SP9–Syt1 C2B (left) and P9–Syt1 C2B (right) superimposed onto the structure of the primary interface (grey). The simulations started from a conformation (Extended Data Fig. 2f, g) that was derived from the crystal structure PDB 5W5C (Supplementary Videos 1 and 2). For one simulation of P9–Syt1 C2B, the P9 peptide dissociated around 168 ns.Source data