Study explores how bacteria become drug resistant

Graphic summary. Credit: DOI: 10.1038 / s41589-021-00936-x

Researchers at Vanderbilt University and the University of Arizona have revealed more of the inner workings of the two-stage “molecular motor” in the cell membrane that enables bacteria to become drug-resistant.

Their findings, which were recently reported in the journal chemical nature biology, will help in the search for inhibitors that can “turn off” the protein, called the ABC transporter. They also direct efforts to block the human version of the vector that enables cancer cells to become resistant to chemotherapy.

“We put this story together from different vectors and ask the question, How did nature engineer this specific molecular motor?” Hasan Meshwarib of Vanderbilt, Ph.D., co-author of the paper with Thomas Tomasiak, Ph.D., of the University of Arizona in Tucson said.

He said understanding how carriers operate is essential to developing drugs to prevent them.

Mishwarb is a pioneer in the study of protein dynamics and is the Louise P. McGavock Professor in the Department of Molecular Physiology and Biophysics at Vanderbilt. Tomasiak has a Ph.D. He received his Ph.D. in pharmacology at Vanderbilt in 2011 and is an assistant professor of chemistry and biochemistry at the University of Arizona.

According to the US Centers for Disease Control and Prevention, antibiotic-resistant bacteria and fungi infect at least 2.8 million people in the United States each year and cause more than 35,000 deaths.

The primary means of resistance is a multidrug ABC source (ATP-binding cassette). ABC exporters use ATP hydrolysis—the release of chemical energy stored in ATP molecules—to move a variety of molecules across cell membranes.

ATP energy provides the ABC exporters with the strength to bind toxic chemicals, then turn around and expel them from the cell. However, in the case of antibiotic-resistant bacteria, this method of survival can be lethal to the human host it invaded.

In 2014, Mechorib’s team, in collaboration with researchers at the University of Illinois at Urbana-Champaign, used a technique called electron magnetic resonance (EPR) spectroscopy to identify previously unreported changes in the shape or morphology of the ABC source from bacteria. It is called Bacillus subtilis because it reacts with ATP.

They suggested that the strength of ATP, in a series of complex steps, drives the transition between the intrinsic and extrinsic conformations of the source. After binding the antibiotic, for example, the source “turns around” to get its payload out of the cell.

This movement is driven by the conversion (conversion) of chemical energy into mechanical energy resulting from the asymmetric and sequential association of two ATP molecules with different parts of the protein complex (ATP-binding strands). The asymmetric association thus leads to the harmonic change.

To prove their theory, the researchers had to take a picture of the harmonic change. So they turned to another source, cryogenic electron microscopy, which allows atomic distances to be measured at frigid temperatures, below minus 320 degrees Fahrenheit.

cryo-EM studies were performed at the Pacific Northwest Center for Cryo-EM in Portland, Ore. Combined with an EPR spectroscopy method called DEER and molecular dynamics simulations, studies have revealed for the first time an ATP-loaded, inwardly oriented structure with two asymmetrically linked drug molecules.

“In 2014, we had indirect evidence,” Masharib said. Now, with cryo-EM, we can say, ‘Here in atomic detail is what’s going on. “

He added that the intermediate form suggests that drugs could be designed to prevent the source of bacteria from turning around and expelling the antibiotic by “trapping” it in its internal state.

Mobile Multidrug Flow Pump

more information:
Tarjani M. Thaker et al., Asymmetric binding of drugs in an ATP-loaded inward facing state of the ABC transporter, chemical nature biology (2021). DOI: 10.1038 / s41589-021-00936-x

Presented by Vanderbilt University

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