Function and frustration of multi-drug ABC exporter protein and design of model proteins for drug delivery using protein hydration thermodynamics.

The mechanism is presented whereby simultaneous hydrolysis of two molecules of ATP in the ATP-binding cassette (ABC) exporter protein, Sav 1866, opens a transmembrane channel to pump drug out of the cell and confers drug resistance, e.g., gives rise to methicillin resistant Staphylococcus aureus, MRSA. The proposed mechanism suggests pharmaceutical design strategies for overloading the capacity of two molecules of ATP to open access to the channel for export. Structural homology of Staphylococcus aureus, Sav 1866, to human P-glyco-protein and MRP2, suggests a similar mechanism could be relevant to human carcinoma cells. The transport mechanism utilizes two thermodynamic quantities -DeltaG(HA), the change in Gibbs free energy for hydrophobic association, and DeltaG(ap), an apolar-polar repulsive free energy for hydration, derived from studies on designed elastic-contractile model proteins (ECMPs). These quantities also allow design of remarkably biocompatible ECMPs as drug delivery vehicles with remarkable control of release profiles and of ECMPs that provide the means of developing pharmaceuticals for blocking multi-drug resistance.