Figure 3(A) Graphical view of the in silico sampling percentage of P31-43 and of P31-43/4QA (4QA) against NBD1. (B) SPR analysis of 4QA peptide on rhNBD1 covalently bound to CM5 sensor chip. Incubation of Caco-2 cells with P31-43 or with modified P31-43 (P31-43-2QA 4-5th or P31-43-2QA 10-11th or P31-43/4QA mutant (4QA) peptides) for 1 h. (C) Immunoprecipitation in non-reducing and non-denaturing conditions of CFTR protein and immunblot with streptavidin-HRP or CFTR antibody (n=3 independent experiments). Mean ± SD of samples assayed. °°p<0.01 vs P31-43 challenge, ***p<0.001 vs Caco-2 challenged with 4QA (ANOVA, Bonferroni post hoc test). Data information: The blots are representative of one experiment for group of treatment. Incubation of Caco-2 cells with P31-43 or with modified P31-43 (P31-43-2QA 4-5th or P31-43-2QA 10-11th or P31-43/4QA mutant (4QA) peptides) for 1 h. (D) Representative traces of CFTR-dependent Cl- secretion measured by forskolin (Fsk)-induced increase of chloride current (Isc (μA/cm2)) in Caco-2 cells mounted in Ussing chambers; quantification of the peak CFTR inhibitor 172 (CFTRinh172)-sensitive Isc (∆Isc) in Caco-2 cells (n= 3 independent experiments). Mean ± SD of samples assayed. °°p<0.01 vs P31-43 challenge, ***p<0.001 vs Caco-2 challenged with 4QA (ANOVA, Bonferroni post hoc test). (E) In vitro Blue native PAGE western blotting of enhanced binding of P31-43 to rhNBD1 in the presence of activated rTG2 that in turn promotes the formation of higher molecular weight complexes. As described in the text, only P31-43 (lanes 1, 3, 5), and not P57-68 (lanes 2, 4, 6), has the ability to form stable complexes with NBD1 and TG2 (n=3 independent experiments). Data information: The blots are representative of one experiment for group of treatment. Incubation of Caco-2 cells with P31-43, in the presence or absence of pre-treatment with TG2 inhibitor Z-DON, TG2-siRNA Immunoprecipitation in non-reducing and non-denaturing conditions of CFTR protein and immunoblot with anti-isopeptide glutamime-lysine and CFTR Incubation of Caco-2 cells with P31-43 in the presence or absence of pre-treatment with TG2 inhibitor Z-DON BAPTA-AM immunoprecipitation of CFTR and then immunoblot with anti-TG2 or anti-CFTR antibodies Incubation of Caco-2 cells with P31-43, in the presence or absence of pre-treatment with TG2 inhibitor Z-DON or VX-770. Effects of treatment with VX-770 and Z-DON on TG2 transamidating activity in situ. (H) In situ detection of TG2 activity in Caco-2 cells pulsed with Ca2+ by immunoblotting of the TG-catalyzed incorporation of 5-biotinamidopentylamine (BAP) and blotting with anti-biotin antibody (n=3 independent experiments). Mean±SD of triplicates of independent experiments. **p<0.01 vs P31-43, °°p<0.001 vs VX-770 (ANOVA, Bonferroni post hoc test). Data information: The blots are representative of one experiment for group of treatment. Incubation of Caco-2 cells with P31-43, in the presence or absence of pre-treatment with TG2 inhibitor Z-DON VX-770. Effects of treatment with VX-770 and Z-DON on TG2 transamidating activity in situ. (I) Assay of TG2 activity by immunostaining of the TG-catalysed incorporation of monodansylcadaverin in Caco-2 cells pre-treated with VX-770 or Z-DON and then pulsed with P31-43. Scale bar, 50µm. Mean±SD of triplicates of independent experiments. **p<0.01 vs P31-43, °°p<0.001 vs VX-770 (ANOVA, Bonferroni post hoc test). Data information: The blots are representative of one experiment for group of treatment. Incubation of Caco-2 cells with P57-68 or P31-43, in the presence or absence of pre-treatment with VX-770. (J) Immunoprecipitation of CFTR and immunoblot with anti-CFTR and anti-TG2 antibodies. Mean±SD of triplicates of independent experiments. **p<0.01 vs P31-43, °°p<0.001 vs VX-770 (ANOVA, Bonferroni post hoc test). Data information: The blots are representative of one experiment for group of treatment. Incubation of Caco-2 cells with P57-68 or P31-43, in the presence or absence of pre-treatment with VX-770. (K) Immunoprecipitation in non-reducing and non-denaturing conditions of PKAr2α protein and immunoblot with isopeptide glutamine-lysine and PKAr2α antibodies (n=3 independent experiments). Mean±SD of triplicates of independent experiments. **p<0.01 vs P31-43, °°p<0.001 vs VX-770 (ANOVA, Bonferroni post hoc test). Data information: The blots are representative of one experiment for group of treatment. Incubation of Caco-2 cells with P57-68 or P31-43, in the presence or absence of pre-treatment with VX-770. (L) Immunoblot of phospho-PKA (phPKA) protein; densitometric analysis of protein levels relative to β-actin. Mean±SD of triplicates of independent experiments. **p<0.01 vs P31-43, °°p<0.001 vs VX-770 (ANOVA, Bonferroni post hoc test). Data information: The blots are representative of one experiment for group of treatment.