Aquaporin 6 binds calmodulin in a calcium-dependent manner.

Aquaporin 6 (AQP6) is an anion channel that is expressed primarily in acid secreting α-intercalated cells of the kidney collecting duct. In addition, AQP6 anion channel permeability is gated by low pH. Inspection of the N-terminus of AQP6 revealed a putative calmodulin binding site. AQP6-expressing CHO-K1 cell lysates were mixed with calmodulin beads and AQP6 was pulled down in the presence of calcium. Mutagenesis of the N-terminal calmodulin binding site in full length mouse AQP6 resulted in a loss of calmodulin binding activity. Mouse and human AQP6 calmodulin binding site peptides bound dansyl-calmodulin with a dissociation constant of approximately 1 μM. The binding of AQP6 to calmodulin may be an important key to determining the physiological role of AQP6 in the kidney.