Members of this protein family are antiporters that exchange histidine with histamine, product of histidine decarboxylation. A system consisting of this protein, and a histidine decarboxylase encoded by an adjacent gene, creates decarboxylation/antiport proton-motive cycle that provides a transient resistance to acidic conditions.
Jiyao W et al.(2023). "The conserved domain database in 2023.",