Identification of putative binding sites of P-glycoprotein based on its homology model.

A homology model of P-glycoprotein based on the crystal structure of the multidrug transporter Sav1866 is developed, incorporated into a membrane environment, and optimized. The resulting model is analyzed in relation to the functional state and potential binding sites. The comparison of modeled distances to distances reported in experimental studies between particular residues suggests that the model corresponds most closely to the first ATP hydrolysis step of the protein transport cycle. Comparison to the protein 3D structure confirms this suggestion. Using SiteID and Site Finder programs three membrane related binding regions are identified: a region at the interface between the membrane and cytosol and two regions located in the transmembrane domains. The regions contain binding pockets of different size, orientation, and amino acids. A binding pocket located inside the membrane cavity is also identified. The pockets are analyzed in relation to amino acids shown experimentally to influence the protein function. The results suggest that the protein has multiple binding sites and may bind and/or release substrates in multiple pathways.