CFTR and MDR: ABC Transporters with Homologous Structure but Divergent Function

While a gene family by definition will have homologies in sequence, the “functional genomics” or characterization of the functionality of siblings can reveal significant differences. One gene family that shares an ATPbinding cassette (ABC) sequence motif is comprised of members named “ABC Transporters.” Until 1989, the members of this family were primarily ATPases that pumped compounds out of cells and many were linked to multidrug resistance (MDR). Hence, at that time the function of the members of the ABC gene family appeared equally homologous to their structure. Since then the discovery of new members, like the cystic fibrosis transmembrane conductance regulator (CFTR) Cl channel and the sulfonylurea receptor (SUR), increased diversity and the homologous structure seemed to no longer link to homologous function. In this mini-review we will introduce two parallel investigations, separated by 10 years, where researchers re-examined the functionality of the human ABC transporters, CFTR and MDR, under the hypothesis that the structurally similar ABC transporters must have similarities in function.