ATP-binding cassette proteins Common denominators between ion channels, transporters, and enzymes

Transporters and ion channels are highly specialized and functionally divergent molecules. However, these proteins may be less structurally diverse than previously appreciated. This is clearly apparent for one superfamily of molecules, the so-called ATP-binding cassette (ABC) proteins, which behave as ATP-dependent ion channels and/or transporters for a wide variety of substrates. ABC proteins also share common structural motifs with voltage-gated ion channels, transporters for glucose and neurotransmitters, and even adenylylcyclase. Beyond this, agents such as verapamil and forskolin, which inhibit and bind to one ABC protein (P-glycoprotein), may interact in homologous domains compared with some of these related proteins. Comparisons between these proteins are likely to provide a general understanding of pores in the lipid bilayer as well as specific properties that allow regulated movement and/or hydrolysis of selected substrates. This knowledge is important since certain ABC family members play a role in normal function and disease and provide novel therapeutic targets for drug development.