Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Rice, Iowa state biologists search for ’half-fusion’

17.05.2005


Study shows illusive ’hemifusion’ state can precede membrane merger



Every living cell is surrounded by a membrane, a thin barrier that separates the genetic machinery of life from the non-living world outside. Though barriers, membranes are not impervious. Cells use a complex hierarchy of proteins that work in concert to allow cell membranes to fuse – with other cells or with membrane-encased packages of proteins and other chemicals that the cell needs to take in or release.

Though well-studied, the molecular details of membrane fusion remain mysterious. In particular, scientists don’t understand how holes form between two membranes, but a new study by biochemists at Rice University and Iowa State University offers intriguing new clues about the nature of this process. The study is published in this month’s issue of Nature Structural and Molecular Biology.


"Membrane fusion is one of the most basic processes of life," said James McNew, assistant professor of biochemistry and cell biology at Rice University. "It begins at fertilization and occurs billions of times a second in our bodies, and if it ever stops, we die."

For example, inside the cells in our brains, spines and nerves, membranes are used to seal up and transport tiny packets of signaling chemicals from the center of the cell to the outer cell membrane. These packets, or vesicles, wait just inside the cell membrane for the appropriate signal, and once they receive it, they fuse with the membrane and eject their contents into the surrounding tissue, causing an immediate chain reaction that keeps our hearts beating and allows us to move our muscles. Membrane fusion is also used to initiate disease. "Some invading organisms like enveloped viruses use the fusion process to infect the cell," McNew said.

To understand membrane fusion, it helps to envision the basic structure of membranes. Just five billionths of meter across, membranes are bilayers, meaning they contain two separate layers, or sheets of fatty acids. Each of these sheets has a one side that is strongly attracted to water and one side that strongly repels it. The water-hating sides of the sheets stick tightly to one another, sealing out water on either side of the bilayer.

Additionally, all biological membranes are dotted with proteins, and some of these are called transmembrane proteins, meaning parts of them penetrate through the membrane like a needle through cloth. A large body of evidence suggests that a class of transmembrane proteins called SNAREs are responsible for driving membrane fusion during normal cellular activity. Exactly how they do this is unknown, but previous studies have suggested two possibilities.

One model proposes that the portion of the SNARE protein that crosses the membrane forms a pore-like connection that mixes both layers of the membrane in one step. The other theory suggests that the SNARE proteins mix the two separate layers of a membrane one at a time, generating an intermediate stated called "hemifusion" or half-fusion. During hemifusion, the outer, water-loving sides of two membranes become connected, and the inner water-loving layers do not. In this state, the combining cells or vesicles could transfer proteins and other material stuck to their outside layers, but they do not exchange any material that’s locked inside. Hemifusion has been observed in non-biological membranes containing no proteins, but has been difficult to detect with SNARE proteins.

McNew and his Iowa State colleagues, Yeon-Kyun Shin, Zengliu Su, Fan Zhang and Yibin Xu, developed an ingenious method of tagging both inner and outer portions of the synthetic membranes with fluorescent dyes so they could use fluorescence spectroscopy to assay mixing of the inner and outer layers.

McNew and colleagues sought to find out if hemifusion was an intermediate fusion state in biological systems, so they created a test system that contained a lipid bilayer studed with SNARE proteins taken from bakers yeast. Using both normal SNAREs and a mutant variety, they were able to show that membrane fusion catalyzed by the SNARE machinery mixes the outer layer of the membrane separately from the inner layer -- a hallmark of hemifusion -- suggesting that a hemifusion intermediate can exist in biological systems and may well be the mechanism that all living cells utilize.

Preliminary data from follow-up studies indicate that these results are also generalizable to SNARE proteins from animals.

Jade Boyd | EurekAlert!
Further information:
http://www.rice.edu

More articles from Studies and Analyses:

nachricht New study from the University of Halle: How climate change alters plant growth
12.01.2018 | Martin-Luther-Universität Halle-Wittenberg

nachricht Disarray in the brain
18.12.2017 | Universität zu Lübeck

All articles from Studies and Analyses >>>

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

Thanks for the memory: NIST takes a deep look at memristors

22.01.2018 | Materials Sciences

Radioactivity from oil and gas wastewater persists in Pennsylvania stream sediments

22.01.2018 | Earth Sciences

Saarland University bioinformaticians compute gene sequences inherited from each parent

22.01.2018 | Life Sciences

VideoLinks Wissenschaft & Forschung
Overview of more VideoLinks >>>