Interaction of Calmodulin and Other Calcium-Modulated Proteins with Gap Junctions

This chapter focuses on the interaction of calmodulin with gap junctions. Gap junctions are plasma membrane specializations formed between contacting cells consisting of an array of subunits, connexons; and containing an aqueous channel between the cells, which is insulated from the extracellular space. Hence, cells containing gap junctions are able to communicate directly with each other by the intercellular diffusion of hydrophilic molecules limited in size by the diameter of the channel. The interaction of calmodulin and other calcium-modulated proteins with purified gap junction proteins from rat liver and bovine lens is examined by the gel overlay procedure. The gap junction polypeptides bind to other calcium-modulated proteins, including troponin C, S-100β, and parvalbumin. The binding of iodinated troponin C and S-100β shows no calcium dependence, whereas the binding of iodinated parvalbumin is enhanced in the presence of chelator. The observed interaction of the junction proteins with these calcium-modulated proteins is consistent with data in other systems where it has been found that these proteins can sometimes substitute for calmodulin in modulating activity of proteins.