Fig. 1: The overall structure and the arrangement of transmembrane helices of human AE3.

a and b Functional comparison of AE2 and AE3 in regulating intracellular pH. Changes in intracellular pH upon Cl⁻ reintroduction were monitored in SLC4A2-KO HEK293F cells overexpressing the human SLC4A2 or SLC4A3 genes, both in the presence and absence of the DIDS inhibitor (40 μM). Cells without overexpression served as controls. All experiments replicated independently three times to ensure consistency. One-way ANOVA with Tukey’s multiple comparisons test was performed, ****p < 0.0001. Source data are provided as a Source Data file. c The cryo-EM density map of \({{\rm{hAE}}}{3}^{{{{\rm{HCO}}}}_{3}-}\) viewed parallel to the cell membrane (left) and from the extracellular perspective (right). The cryo-EM density map corresponding to two protomers in dimeric \({{\rm{hAE}}}{3}^{{{{\rm{HCO}}}}_{3}-}\) were highlighted in red (chain A) and blue (chain B), respectively. Non-protein densities within the TMDs are depicted in gray, with lipid molecules and unresolved protein segments in green. d The dimeric architecture of \({{\rm{hAE}}}{3}^{{{{\rm{HCO}}}}_{3}-}\) TMD aligned with the orientation of the EM map above. The protomer B was colored in blue and protomer A was colored by helices in a rainbow gradient. e The cartoon representation of dimeric structure of \({{\rm{hAE}}}{3}^{{{{\rm{HCO}}}}_{3}-}\) TMD viewed from the same perspective as the EM map. f Topological diagram of the hAE3 monomer, with TM helices color-matched to those in Fig. 1d. Disease-associated mutation sites are indicated with circles and red font. g Arrangement of transmembrane helices in hAE3, viewed from the extracellular side, illustrating the spatial organization of the helices.