Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Protein-hungry cells ’go fishing,’ report Purdue biologists

26.11.2003


Shown in this graphic is the protein colicin and the receptors it uses to cross the cellular membrane of an E. coli bacterium. After lodging one of its ends in the "BtuB" receptor, usually used to admit vitamin B12 into the cell, the protein uses its extended "fishing pole" to search for a porous second receptor, "OmpF," that will allow its import across the membrane. (Kurisu et al., Nature Structural Biology, 2003).

When a cell needs a protein to function, it sometimes uses molecule-sized fishing poles to "catch" one and "cast" it across the cell membrane, reports a research team of Purdue University biologists.

Using high-resolution X-ray crystallography, a team including William A. Cramer has determined the structure and surprising behavior of a protein receptor complex, or "gate," found in the outer membrane of an E. coli bacterium. The complex is one of thousands of such tiny gates that the cell uses to bring substances into its cytoplasm, or interior. The team also determined the structure of one such substance, a protein called colicin, that the gate admits into the E. coli, marking a first for the biological field.

"This represents the first time we have seen a receptor complex and its corresponding importable protein up close," said Cramer, who is Henry Koffler Distinguished Professor of Biological Sciences in Purdue’s School of Science. "While we have seen the gates before as a group, we have never seen how an individual gate works to bring a protein inside. This information could tell us a lot about our own metabolism."

The research, which appears in the November issue of Nature Structural Biology, was performed by a team including lead authors Genji Kurisu, Stanislav Zakharov and Masha Zhalnina. Also contributing was Michael Wiener of the University of Virginia’s Department of Molecular Physiology and Biological Physics.

The group’s work turned up some unusual details about cellular commerce, the business an E. coli cell conducts with the outside world through its membrane. With hundreds of protein receptors serving as gate guards, the membrane admits into the cytoplasm the nutrients the cell needs to exist. In most cases, receptors are made to admit only one particular substance.

"If you’ve ever seen the game ’Perfection,’ in which you have to put a number of uniquely shaped pegs into their corresponding holes before time runs out, you have a general idea of how these receptors are laid out in the cell membrane," Cramer said. "There are hundreds of receptor types, each of which is built to admit one thing – iron or sugar molecules, for example."

But while the receptor Cramer’s team analyzed was made to admit the vitamin B-12, the researchers found that colicin could enter the E. coli by "parasitizing" the receptor for its own use.

"Its method, at first, seems a bit unorthodox," Cramer said. "Colicin essentially has two parts connected to one another by a long rod, and it cannot fit through a single hole in the membrane. So once it finds its first hole, it has to go fishing for another."

One of the colicin’s halves binds to the vitamin B-12 receptor, while its tail end remains hanging from the membrane like a long fishing rod. The B-12 receptor then essentially swings the tail around until it finds what it needs – the second receptor that can admit the rest of the colicin.

"This two-receptor approach may appear to be a strange way to do business," Cramer said, "but we theorize that it is actually the norm, rather than the exception, when it comes to getting proteins across membranes."

While this is the only example thus far of how a protein uses receptors, Cramer said that evidence for the theory lies in the organization of the receptors in the membranes themselves.

"Receptors tend to lie together in clusters," he said. "Biologists have long found a concentration of one type of receptor mixed in with a few other types, much as elephants and giraffes congregate on the plains, while other species are found in the forest. But here, it’s not terrestrial ecology at work – we think the receptors lie close together because proteins need more than one to get inside."

Another unusual aspect of the research was the nature of the protein itself. Ordinarily, a cell will admit only beneficial substances, but colicin is actually toxic to the E. coli once it penetrates the membrane.

"Colicin fools the membrane, and can actually kill the bacterium once it’s inside," Cramer said. "We, of course, also would like to find out how the cell ingests a helpful protein rather than a poisonous one, but this is the only protein we know that can fool the receptor complex we managed to isolate for this study."

Membrane proteins have proven to be notoriously difficult to study (see related articles), but Cramer’s team has had a string of successful research on these molecules, which perform many functions related to metabolism in living things.

"If we can find out more about how these membrane proteins work, we may gain fundamental insights into how your body obtains energy from the environment," Cramer said. "Strength, endurance, health – they’re all essentially metabolic processes, and figuring out how these processes change as we age will almost certainly depend on figuring out how membrane proteins do their jobs."

Members of Cramer’s research team are affiliated with several research centers at Purdue, including the Markey Center for Structural Biology, the Bindley Bioscience Center at Discovery Park, the Interdepartmental Program in Biochemistry and Molecular Biology, and the Purdue Cancer Center.

Funding for this research was provided mainly by the National Institutes of Health.

Writer: Chad Boutin, (765) 494-2081, cboutin@purdue.edu

Source: William Cramer, (765) 494-4956, wac@bilbo.bio.purdue.edu

Chad Boutin | Purdue News
Further information:
http://news.uns.purdue.edu/html4ever/031125.Cramer.ecoli.html

More articles from Life Sciences:

nachricht Multifunctional Platform for the Delivery of Gene Therapeutics
22.01.2018 | Angewandte Chemie International Edition

nachricht Charge Order and Electron Localization in a Molecule-Based Solid
22.01.2018 | Max-Planck-Institut für Chemische Physik fester Stoffe

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Artificial agent designs quantum experiments

On the way to an intelligent laboratory, physicists from Innsbruck and Vienna present an artificial agent that autonomously designs quantum experiments. In initial experiments, the system has independently (re)discovered experimental techniques that are nowadays standard in modern quantum optical laboratories. This shows how machines could play a more creative role in research in the future.

We carry smartphones in our pockets, the streets are dotted with semi-autonomous cars, but in the research laboratory experiments are still being designed by...

Im Focus: Scientists decipher key principle behind reaction of metalloenzymes

So-called pre-distorted states accelerate photochemical reactions too

What enables electrons to be transferred swiftly, for example during photosynthesis? An interdisciplinary team of researchers has worked out the details of how...

Im Focus: The first precise measurement of a single molecule's effective charge

For the first time, scientists have precisely measured the effective electrical charge of a single molecule in solution. This fundamental insight of an SNSF Professor could also pave the way for future medical diagnostics.

Electrical charge is one of the key properties that allows molecules to interact. Life itself depends on this phenomenon: many biological processes involve...

Im Focus: Paradigm shift in Paris: Encouraging an holistic view of laser machining

At the JEC World Composite Show in Paris in March 2018, the Fraunhofer Institute for Laser Technology ILT will be focusing on the latest trends and innovations in laser machining of composites. Among other things, researchers at the booth shared with the Aachen Center for Integrative Lightweight Production (AZL) will demonstrate how lasers can be used for joining, structuring, cutting and drilling composite materials.

No other industry has attracted as much public attention to composite materials as the automotive industry, which along with the aerospace industry is a driver...

Im Focus: Room-temperature multiferroic thin films and their properties

Scientists at Tokyo Institute of Technology (Tokyo Tech) and Tohoku University have developed high-quality GFO epitaxial films and systematically investigated their ferroelectric and ferromagnetic properties. They also demonstrated the room-temperature magnetocapacitance effects of these GFO thin films.

Multiferroic materials show magnetically driven ferroelectricity. They are attracting increasing attention because of their fascinating properties such as...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

10th International Symposium: “Advanced Battery Power – Kraftwerk Batterie” Münster, 10-11 April 2018

08.01.2018 | Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

 
Latest News

Multifunctional Platform for the Delivery of Gene Therapeutics

22.01.2018 | Life Sciences

The world's most powerful acoustic tractor beam could pave the way for levitating humans

22.01.2018 | Power and Electrical Engineering

Siberian scientists learned how to reduce harmful emissions from HPPs

22.01.2018 | Power and Electrical Engineering

VideoLinks