Water channel activities of Mimosa pudica plasma membrane intrinsic proteins are regulated by direct interaction and phosphorylation

cDNAs encoding aquaporins PIP1;1, PIP2;1, and TIP1;1 were isolated from Mimosa pudica (Mp) cDNA library. MpPIP1;1 exhibited no water channel activity; however, it facilitated the water channel activity of MpPIP2;1 in a phosphorylation-dependent manner. Mutagenesis analysis revealed that Ser-131 of MpPIP1;1 was phosphorylated by PKA and that cooperative regulation of the water channel activity of MpPIP2;1 was regulated by phosphorylation of Ser-131 of MpPIP1;1. Immunoprecipitation analysis revealed that MpPIP1;1 binds directly to MpPIP2;1 in a phosphorylation-independent manner, suggesting that phosphorylation of Ser-131 of MpPIP1;1 is involved in regulation of the structure of the channel complex with MpMIP2;1 and thereby affects water channel activity.