Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

TSRI Scientists Illuminate Mysterious Molecular Mechanism Powering Cells in Most Forms of Life

09.01.2015

A team led by structural biologists at The Scripps Research Institute (TSRI) has taken a big step toward understanding the intricate molecular mechanism of a metabolic enzyme produced in most forms of life on Earth.

The finding, published in the January 9 issue of Science, concerns nicotinamide nucleotide transhydrogenase (TH), an ancient evolutionary enzyme found throughout the animal kingdom as well as in plants and many simpler species. The enzyme is part of a process key to maintaining healthy cells and has also recently been linked to diseases such as diabetes and cancer.


Image by Josephine Leung, courtesy of the Stout lab, The Scripps Research Institute.

The new study provides insight into how a critical mitochondrial enzyme, transhydrogenase (TH), works in a process that is key to maintaining healthy cells.

“Despite its importance, TH has been one of the least-studied of mitochondrial enzymes,” said TSRI Associate Professor C. David Stout. “Our new study helps clear up some mysteries—suggesting how the enzyme structure might harness protons and indicating that its two sides are able to alternate functions, always staying in balance.”

Powering the Cell

In humans and other higher organisms, TH enzymes work within mitochondria, the tiny, double-hulled oxygen reactors that help power most cellular processes.

As a mitochondrion burns oxygen, it pumps protons (hydrogen atoms denuded of their electrons) out of its inner compartment (“matrix”), creating an excess of these charged particles just outside its inner membrane. TH enzymes, which are fixed at one end within this membrane, allow a one-by-one flow of protons back through the membrane within the matrix. This process—which is similar to that which makes ATP, the cell’s universal source of energy—has also been linked to the production of a compound called NADPH, which is crucial for defusing oxygen free radicals to maintain cell health.

Stout’s laboratory and others have previously described portions of the TH enzyme that protrude from the membrane into the mitochondrial matrix. But a precise understanding of TH’s mechanism has been elusive. In its entirety, the enzyme has an exceptionally loose structure that makes it hard to evaluate using X-ray crystallography, the standard tool for determining the structures of large proteins at atomic-level resolution.

“Key details we’ve been lacking include the structure of TH’s transmembrane portion, and the way in which the parts assemble into the whole enzyme,” said Josephine H. Leung, a graduate student in the Stout laboratory who was lead author of the study.

New Clues to a Dynamic Structure

In the new study, thanks to technology developed by Professor Vadim Cherezov, now of University of Southern California, Leung and her colleagues were able for the first time to form crystals (neatly lined-up groupings) of the TH transmembrane portion and use X-ray crystallography to determine its structure—to an atomic-level resolution of 2.8 angstroms (280 trillionths of a meter).

The team also was able to grow crystals of the whole TH enzyme. These yielded a much lower-resolution structural image, but the researchers were able to enhance the resolution to 6.9 angstroms by plugging in data from crystallography of individual TH portions. In a further study, Professor Bridget Carragher and colleagues at the TSRI-based National Resource for Automated Molecular Microscopy (NRAMM) imaged individual copies of the enzyme to 18 angstroms using electron microscopy. Stout emphasized that such seamless collaborations at TSRI made this work possible: “Only an environment as at Scripps would enable the study of transhydrogenase.”

The electron microscopy data confirmed that TH naturally exists as a “dimer”—two identical copies bound together—and provided major clues to how TH manages to work in this conformation.

Directly above TH’s transmembrane structure, just inside the mitochondrial matrix, is the “domain III” structure that binds NADPH’s precursor molecule, NADP+, during conversion to NADPH. Structural biologists haven’t understood how two such structures could work side by side in the TH dimer and not interfere with each other’s activity. The new structural data suggest that these side-by-side structures are highly flexible and always have different orientations.

“Our most striking finding was that the two domain III structures are not symmetric—one of them faces up while the other faces down,” said Leung.

In particular, one of structures is oriented apparently to catalyze the production of NADPH, while the other is turned towards the membrane, perhaps to facilitate transit of a proton. The new structural model suggests that with each proton transit, the two domain III structures flip and switch their functions. “We suspect that the passage of the proton is what somehow causes this flipping of the domain III structures,” said Leung.

But much work remains to be done to determine TH’s precise structure and mechanism. For example, the new structural data provide evidence of a likely proton channel in the TH transmembrane region, but show only a closed conformation of that structure. “We suspect that this channel can have another, open conformation that lets the proton pass through, so that’s one of the details we want to study further,” said Leung.

“There are many experiments to follow,” Stout said.

Other co-authors of the study, “Division of labor in transhydrogenase by alternating proton translocation and hydride transfer,” were Robert B. Gennis, professor of biochemistry and biophysics at the University of Illinois at Urbana-Champaign, and a research associate in his laboratory, Lici A. Schurig-Briccio, who produced whole TH proteins for analysis and characterized the activity of TH when mutated at key structural sites; Jeffrey A. Speir of NRAAM; former NRAAM member Arne Moeller, now at Aarhus University; and Mutsuo Yamaguchi, staff scientist in the Stout laboratory at TSRI.

Support for the study was provided by the National Institutes of Health (5R01GM061545) and by the National Institute of General Medical Sciences (1R01GM103838, GM095600, GM073197 and P41GM103310).

About the Scripps Research Institute

The Scripps Research Institute (TSRI) is one of the world's largest independent, not-for-profit organizations focusing on research in the biomedical sciences. TSRI is internationally recognized for its contributions to science and health, including its role in laying the foundation for new treatments for cancer, rheumatoid arthritis, hemophilia, and other diseases. An institution that evolved from the Scripps Metabolic Clinic founded by philanthropist Ellen Browning Scripps in 1924, the institute now employs about 3,000 people on its campuses in La Jolla, CA, and Jupiter, FL, where its renowned scientists—including three Nobel laureates—work toward their next discoveries. The institute's graduate program, which awards PhD degrees in biology and chemistry, ranks among the top ten of its kind in the nation. For more information, see www.scripps.edu

Madeline McCurry Schmidt | newswise

More articles from Life Sciences:

nachricht Water forms 'spine of hydration' around DNA, group finds
26.05.2017 | Cornell University

nachricht How herpesviruses win the footrace against the immune system
26.05.2017 | Helmholtz-Zentrum für Infektionsforschung

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 the immune system be boosted against Staphylococcus aureus by delivery of messenger RNA?

Staphylococcus aureus is a feared pathogen (MRSA, multi-resistant S. aureus) due to frequent resistances against many antibiotics, especially in hospital infections. Researchers at the Paul-Ehrlich-Institut have identified immunological processes that prevent a successful immune response directed against the pathogenic agent. The delivery of bacterial proteins with RNA adjuvant or messenger RNA (mRNA) into immune cells allows the re-direction of the immune response towards an active defense against S. aureus. This could be of significant importance for the development of an effective vaccine. PLOS Pathogens has published these research results online on 25 May 2017.

Staphylococcus aureus (S. aureus) is a bacterium that colonizes by far more than half of the skin and the mucosa of adults, usually without causing infections....

Im Focus: A quantum walk of photons

Physicists from the University of Würzburg are capable of generating identical looking single light particles at the push of a button. Two new studies now demonstrate the potential this method holds.

The quantum computer has fuelled the imagination of scientists for decades: It is based on fundamentally different phenomena than a conventional computer....

Im Focus: Turmoil in sluggish electrons’ existence

An international team of physicists has monitored the scattering behaviour of electrons in a non-conducting material in real-time. Their insights could be beneficial for radiotherapy.

We can refer to electrons in non-conducting materials as ‘sluggish’. Typically, they remain fixed in a location, deep inside an atomic composite. It is hence...

Im Focus: Wafer-thin Magnetic Materials Developed for Future Quantum Technologies

Two-dimensional magnetic structures are regarded as a promising material for new types of data storage, since the magnetic properties of individual molecular building blocks can be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute published their findings in the journal Nature Communications.

Ferrimagnets are composed of two centers which are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets...

Im Focus: World's thinnest hologram paves path to new 3-D world

Nano-hologram paves way for integration of 3-D holography into everyday electronics

An Australian-Chinese research team has created the world's thinnest hologram, paving the way towards the integration of 3D holography into everyday...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Marine Conservation: IASS Contributes to UN Ocean Conference in New York on 5-9 June

24.05.2017 | Event News

AWK Aachen Machine Tool Colloquium 2017: Internet of Production for Agile Enterprises

23.05.2017 | Event News

Dortmund MST Conference presents Individualized Healthcare Solutions with micro and nanotechnology

22.05.2017 | Event News

 
Latest News

How herpesviruses win the footrace against the immune system

26.05.2017 | Life Sciences

Water forms 'spine of hydration' around DNA, group finds

26.05.2017 | Life Sciences

First Juno science results supported by University of Leicester's Jupiter 'forecast'

26.05.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>