Cloning of a novel cDNA homologous to CHIP28 water channel from ocular ciliary epithelium.

Water channel protein (CHIP28) has been initially identified from human erythrocyte and subsequently localized in human kidney, rat kidney and bovine corneal endothelium. We report here cloning of homologous cDNA (CHIP29) from an expression cDNA library constructed from bovine ciliary epithelium poly A+ that codes a 271 amino acid, 28.8 kDa protein. At the amino acid level, bovine CHIP29 is 91% identical to the CHIP28 protein. Analysis of the deduced amino acid sequence indicated a hydrophobic protein with six membrane spanning domains, one N-linked glycosylation site, two conserved NPA boxes common to MIP26 family proteins, and conserved amino acid residue cysteine 189 common to water channels. Northern blotting revealed a major mRNA of 2.8 Kb size expressed in bovine ciliary epithelium. The results presented here confirm the presence of water channel gene in the bovine ciliary epithelium, a primary site for the aqueous humor production.