Conservation and phylogenetic stepwise changes of aquaporin (AQP) 4 palmitoylation in vertebrate evolution

The aquaporin (AQP) family channels control water transport across cell membranes in various organs of mammals. Among 13 AQP family subtypes (AQP0-12), AQP4 is predominantly expressed in the central nervous system. Previous studies revealed that AQP4M1 full-length splice variant is specifically palmitoylated at two cysteine residues (Cys13 and Cys17) in its N-terminus and the palmitoylation of these sites regulates the supramolecular assembly of AQP4 isoforms on the membrane. Here, I further focused on conservation of these palmitoylation sites found in animal AQP4 orthologs. Analysis of sequence databases provides an insight into phylogenetic stepwise changes of AQP4 palmitoylation motifs in vertebrate lineages. AQP4 palmitoylation mechanism itself has been almost completely conserved throughout vertebrate species in spite of the divergence of AQP4 full-length amino acid sequences during molecular evolution. My findings indicate that dynamic regulation of AQP4 made possible by reversible post-translational protein palmitoylation may be critical for the specific refined functions of water transport in the vertebrate central nervous system.