Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Scripps scientists find structure of a protein that makes cancer cells resistant to chemotherapy

31.03.2009
A research team at the Scripps Research Institute has obtained the first glimpse of a protein that keeps certain substances, including many drugs, out of cells.

The protein, called P-glycoprotein or P-gp for short, is one of the main reasons cancer cells are resistant to chemotherapy drugs. Understanding its structure may help scientists design more effective drugs.

The new research was described in the March 27, 2009, issue of the journal Science.

"This structure is an important advance and we hope it is just the beginning of more breakthroughs for us," says the study's senior author Geoffrey Chang, an associate professor at Scripps Research. "The structure is a nice tool for understanding how drugs are transported out of cells by P-gp and for designing drugs to evade P-gp preventing drug resistance. It's very exciting."

P-gp, a protein first identified in 1976, sits in the membrane that surrounds human cells, including those in the gut, intestine, kidney, and brain, where it functions as a gate keeper, shooing out potentially harmful agents. Problematically, P-gp not only transports substances that are harmful out of the cell, but also drugs targeted to cancer cells and HIV-infected cells, as well as some therapeutics aimed at alleviating psychiatric conditions.

"We've long known that P-glycoprotein plays a key role in multidrug resistance in cancer patients, and this work helps us understand how the protein can act on such a wide range of compounds," said Jean Chin, Ph.D., of the National Institutes of Health's (NIH) National Institute of General Medical Sciences (NIGMS), which partially supported the work. "In the future, scientists may be able to use these crystal structures to design chemicals that block P-glycoprotein's activity and restore sensitivity to chemotherapeutic agents."

Solving the Structure

The team, which included scientists from Texas Tech University Health Sciences Center as well as Scripps Research, determined the structure of P-gp using a technique in structural biology known as x-ray crystallography, which involves making crystals of ordered arrays of protein and then blasting the frozen crystals with x-ray radiation. The atoms in the protein crystals cause the x-rays to diffract, and the scientists collect and analyze the pattern of diffraction to solve the atomic-level structure of the proteins.

"The biggest challenge was to get enough protein to purify and make crystals from it," says Stephen Aller, Ph.D., a postdoctoral fellow in Chang's laboratory and first author of the new study.

Once the scientists succeeded in performing the x-ray crystallography and solving the structure, they found that the mouse protein P-gp, which is 87 percent identical to its human counterpart, has the shape of an upside down "v" or a tipi with a large cavity inside. The cavity's interior is lined with amino acids that bind to various substances, holding them in place. The top part of the tipi resides inside the cell membrane and has two openings for substances to enter; the bottom portion sticks out inside the cell, ending in two dumbbell-shaped arms.

This overall shape is strikingly similar to that of another protein, MsbA, that transports lipids out of bacteria. This similarity suggests that P-gp works by bringing the two dumbbell-shaped arms together on the inside of the cell and opening the closed end toward the outside of the cell, essentially reversing direction of the "v" or tipi so any substance caught inside the protein's cavity is ejected from the cell.

While the new study shows another similarity between MsbA and P-gp—both binding cavities are lined with hydrophobic amino acids—it turns out that the mammalian P-gp has many more such amino acids and a greater variety of them, including aromatic amino acids that are known to bind many different substances (substances acted on by enzymes).

"Unlike the bacterial protein, the mammalian P-gp was designed to have a wide range of substrates," says Chang. "The presence of so many hydrophobic and aromatic residues explains how this happens."

A Path to Better Drugs

The new study also produced insights by showing structures of P-gp bound to some of its substrates. Chang and Aller collaborated with Qinghai Zhang, an assistant professor at Scripps Research, who had designed several compounds that can block the function of P-gp. These compounds bind inside the P-gp cavity, preventing other substances from entering. Chang and Aller were able to obtain the structures of two of Zhang's compounds inside P-gp.

"They both go in the same cavity and bind to different amino acids, but with some overlap," says Aller. "What this tells us is that there is an extremely important core set of amino acids in P-gp that bind all substances, and there are additional amino acids for fine-tuning the binding to specific drugs."

Knowing what the P-gp binding cavity looks like and precisely where substances bind may allow researchers design better drugs, for example by using chemistry to modify portions of that drug so that it can sneak past P-gp to get inside cells.

"[One advantage in this process is] we don't have to design brand new drugs, but rather re-design existing ones to make them work better," says Chang. "Scripps is a perfect place for these kinds of studies because there are great chemistry and biology labs here. We can easily find collaborators."

In addition to Chang, Aller, and Zhang, co-authors of the study "Structure of P-glycoprotein reveals a molecular basis for poly-specific drug binding" include Jodie Yu, Andrew Ward, Yue Weng and Srinivas Chittaboina from Scripps Research and Ina L. Urbatsch, Rupeng Zhuo, Patina M. Harrell, and Yenphuong T. Trinh, from Texas Tech University Health Sciences Center in Lubbock Texas.

This research was supported grants from the U.S. Army, the National Institutes of Health, the Beckman Foundation, the Skaggs Institute, Jasper L. and Jack Denton Wilson Foundation, and the Southwest Cancer and Treatment Center, as well as by a scholarship from the People's Republic of China (Weng), a Norton B. Gilula Fellowship (Ward), and a NIGMS National Research Service Award postdoctoral fellowship (Aller).

About The Scripps Research Institute

The Scripps Research Institute is one of the world's largest independent, non-profit biomedical research organizations, at the forefront of basic biomedical science that seeks to comprehend the most fundamental processes of life. Scripps Research is internationally recognized for its discoveries in immunology, molecular and cellular biology, chemistry, neurosciences, autoimmune, cardiovascular, and infectious diseases, and synthetic vaccine development. Established in its current configuration in 1961, it employs approximately 3,000 scientists, postdoctoral fellows, scientific and other technicians, doctoral degree graduate students, and administrative and technical support personnel. Scripps Research is headquartered in La Jolla, California with a second campus in Jupiter, Florida. Research at Scripps Florida focuses on basic biomedical science, drug discovery, and technology development.

Keith McKeown | EurekAlert!
Further information:
http://www.scripps.edu

More articles from Life Sciences:

nachricht How brains surrender to sleep
23.06.2017 | IMP - Forschungsinstitut für Molekulare Pathologie GmbH

nachricht A new technique isolates neuronal activity during memory consolidation
22.06.2017 | Spanish National Research Council (CSIC)

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Quantum thermometer or optical refrigerator?

23.06.2017 | Physics and Astronomy

A 100-year-old physics problem has been solved at EPFL

23.06.2017 | Physics and Astronomy

Equipping form with function

23.06.2017 | Information Technology

VideoLinks
B2B-VideoLinks
More VideoLinks >>>