Introduction
ABC transporters are intricate molecular systems that characterize the vectorial transport of various substrates across biological membranes. They are present in all extant species ranging from prokaryotes to humans (Childs & Ling, 1994; Jones & George, 2004) and comprise the largest family of transmembrane proteins. These transmembrane proteins bind ATP and utilize the energy to drive the active transport of diverse molecules across all cell membranes against the concentration gradient (Dean & Annilo, 2005; Higgins, 1992; KM Moitra, 2012). Characterization of this important class of transporters, which contain one of the largest and ancient protein subfamilies that transport a myriad of substrates from sugars, amino acids, proteins to metal ions, will yield invaluable insights into the molecular basis and physiology of human diseases (Higgins, 1992).