Calmodulin site at the C-terminus of the putative lens gap junction protein MIP26

Lens fiber junctions contain cell-to-cell channels believed to be composed of a 28.2 kD protein (MIP26). Previous evidence indicates that calmodulin (CaM) is involved in the regulation of channel permeability by changing the conformation of the C terminal chain of MIP26. A study of the amino acid sequence of MIP26 has revealed an amphiphilic segment of the C-terminal chain with potential CaM-binding characteristics. To test the capacity of this chain to interact with CaM, a 20-amino acid peptide (peptide C) of appropriate sequence has been synthesized and purified by HPLC. Evidence from spectrofluorometry and circular dichroism experiments indicates that CaM interacts with and affects the conformation of peptide C, suggesting the involvement of MIP26 C-terminal chain and CaM in gating lens junction channels.