ABSTRACT
Traditionally, the aquaporin protein family was functionally divided into water-specific, orthodox aquaporins and neutral solute-permeable aquaglyceroporins. Later, several more physiologically relevant substrates were found to follow the aquaporin permeation path, such as arsenous, boric, and silicic acid that resemble the glycerol molecule, or small gaseous compounds, such as carbon dioxide or ammonia. For the latter, the term aquaammoniaporin was generated. Despite its similarity in terms of physicochemical parameters, hydrogen peroxide was considered rather late as a putative aquaporin permeation substrate. It turned out that the subfamily of aquaammoniaporins exhibits particularly high permeability for hydrogen peroxide. In this chapter, the structural peculiarities of the aquaporin fold and the molecular substrate selectivity mechanisms are highlighted and discussed with respect to hydrogen peroxide permeability. Theoretical and experimental evidence confirms that the aquaammoniaporin selectivity filter layout is optimal for facilitating hydrogen peroxide due to its polarity, hydrogen bond interaction sites, and slightly increased diameter.
