Structural determinants of the hydrogen peroxide permeability of aquaporins

Aquaporins ( AQP ) conduct small, uncharged molecules, such as water (orthodox AQP s), ammonia (aquaammoniaporins) or glycerol (aquaglyceroporins). The physiological functions of AQP s are involved in osmotic volume regulation or the transport of biochemical precursors and metabolic waste products. The recent identification of hydrogen peroxide ( H 2 O 2 ) as a permeant of certain AQP s suggests additional roles in mitigating oxidative stress or enabling paracrine H 2 O 2 signalling. Yet, an analysis of the structural requirements of the H 2 O 2 permeability of AQP s is missing. We subjected a representative set of wild‐type and mutant AQP s to a newly established quantitative phenotypic assay. We confirmed high H 2 O 2 permeability of the human aquaammoniaporin AQP 8 and found intermediate H 2 O 2 permeability of the prototypical orthodox water channel AQP 1 from the rat. Differences from an earlier report showing an absence of H 2 O 2 permeability of human AQP 1 can be explained by expression levels. By generating point mutations in the selectivity filter of rat orthodox aquaporin AQP 1, we established a correlation of H 2 O 2 permeability primarily with water permeability and secondarily with the pore diameter. Even the narrowest pore of the test set (i.e. rat orthodox aquaporin AQP 1 H 180 F with a pore diameter smaller than that of natural orthodox AQP s) conducted water and H 2 O 2 . We further found that H 2 O 2 permeability of the aquaglyceroporin from the malaria parasite P lasmodium falciparum was lower despite its wider pore diameter. The data suggest that all water‐permeable AQP s are H 2 O 2 channels, yet H 2 O 2 permeability varies with the isoform. Thus, generally, AQP s must be considered as putative players in situations of oxidative stress (e.g. in P lasmodium ‐infected red blood cells, immune cells, the cardiovascular system or cells expressing AQP 8 in their mitochondria).