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 New gene potentially involved in metastasis identified
26.03.2019 | Institute of Science and Technology Austria

nachricht Decoding the genomes of duckweeds: low mutation rates contribute to low genetic diversity
26.03.2019 | Westfälische Wilhelms-Universität Münster

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: New gene potentially involved in metastasis identified

Gene named after Roman goddess Minerva as immune cells get stuck in the fruit fly’s head

Cancers that display a specific combination of sugars, called T-antigen, are more likely to spread through the body and kill a patient. However, what regulates...

Im Focus: The taming of the light screw

DESY and MPSD scientists create high-order harmonics from solids with controlled polarization states, taking advantage of both crystal symmetry and attosecond electronic dynamics. The newly demonstrated technique might find intriguing applications in petahertz electronics and for spectroscopic studies of novel quantum materials.

The nonlinear process of high-order harmonic generation (HHG) in gases is one of the cornerstones of attosecond science (an attosecond is a billionth of a...

Im Focus: Magnetic micro-boats

Nano- and microtechnology are promising candidates not only for medical applications such as drug delivery but also for the creation of little robots or flexible integrated sensors. Scientists from the Max Planck Institute for Polymer Research (MPI-P) have created magnetic microparticles, with a newly developed method, that could pave the way for building micro-motors or guiding drugs in the human body to a target, like a tumor. The preparation of such structures as well as their remote-control can be regulated using magnetic fields and therefore can find application in an array of domains.

The magnetic properties of a material control how this material responds to the presence of a magnetic field. Iron oxide is the main component of rust but also...

Im Focus: Self-healing coating made of corn starch makes small scratches disappear through heat

Due to the special arrangement of its molecules, a new coating made of corn starch is able to repair small scratches by itself through heat: The cross-linking via ring-shaped molecules makes the material mobile, so that it compensates for the scratches and these disappear again.

Superficial micro-scratches on the car body or on other high-gloss surfaces are harmless, but annoying. Especially in the luxury segment such surfaces are...

Im Focus: Stellar cartography

The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT) in Arizona released its first image of the surface magnetic field of another star. In a paper in the European journal Astronomy & Astrophysics, the PEPSI team presents a Zeeman- Doppler-Image of the surface of the magnetically active star II Pegasi.

A special technique allows astronomers to resolve the surfaces of faraway stars. Those are otherwise only seen as point sources, even in the largest telescopes...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

International Modelica Conference with 330 visitors from 21 countries at OTH Regensburg

11.03.2019 | Event News

Selection Completed: 580 Young Scientists from 88 Countries at the Lindau Nobel Laureate Meeting

01.03.2019 | Event News

LightMAT 2019 – 3rd International Conference on Light Materials – Science and Technology

28.02.2019 | Event News

 
Latest News

Searching for disappeared anti-matter: A successful start to measurements with Belle II

26.03.2019 | Physics and Astronomy

Extremely accurate measurements of atom states for quantum computing

26.03.2019 | Physics and Astronomy

Listening to the quantum vacuum

26.03.2019 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>