One way that many forms of cancer evade the toxic effects of chemotherapeutic drugs is through expression of the P-glycoprotein. This membrane protein uses energy from the hydrolysis of ATP to transport over 200 structurally distinct compounds, including many drugs, out of the cell. Because of its widespread expression in many tissues of the body the P-glycoprotein also affects the distribution and excretion of a large number of other drugs and toxicants. Consequently, for over 40 years, researchers have attempted to understand the structure and function of the P-glycoprotein in the hope of discovering new ways to productively modulate its activity. Now, Vanderbilt Basic Sciences investigator Hassane Mchaourab, his collaborators Robert Nakamoto (University of Virginia) and Emad Tajkhorshid (University of Illinois at Urbana-Champaign), and their laboratories have learned how the P-glycoprotein harnesses the energy from ATP hydrolysis to propel a substrate molecule across the cell membrane. The Mchaourab laboratory uses a technique called double electron-electron resonance (DEER) to measure the distance between two previously labeled sites on a protein. DEER enables the researchers to monitor changes in this distances that occur as the protein changes from one functional state to another. They discovered that the biggest change in P-glycoprotein structure occurs right at the time of ATP hydrolysis, and that the two sites on the protein where ATP hydrolysis occurs function asymmetrically. These, along with other data, enabled them to use computational methods to construct a model of the protein’s structure just following substrate transport. They were also able to propose a mechanism that describes how ATP hydrolysis leads to a series of structural changes in the protein that result in substrate transport. This important discovery provides new insight into the functioning of P-glycoprotein that may lead to future success in preventing cancer drug resistance. The work is published in the journal Nature [B. Verhalen, R Dastvan, et al., (2017) Nature, published online March 16, 2017, DOI:10.1038/nature21414].