Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Atomic force microscopy : How cell membranes respond to their environment

01.08.2005


Organization of membrane proteins… Membrane organization in photosynthetic bacteria – observed by atomic force microscopy –exposed to strong light. The light-harvesting complexes (small circles) alternate geometrically with the reaction centers (large rings with central density) which manage the light energy. The reaction centers are organized so as to manage light energy, when light is strong.


Some 25% of genes code for membrane proteins. Yet membrane organization remains a mystery. Membranes envelop all the cells in our bodies, forming a natural barrier, the membrane proteins within these can also recognize certain cells and direct a drug to them.

Using atomic force microscopy, Simon Scheuring (Inserm), in a CNRS unit at the Institut Curie, and James N. Sturgis, professor at the Université de la Méditerranée (CNRS unit), have studied the organization of a bacterial membrane and how it adapts in response to external factors. This is the first time that the inner workings of a membrane have been unveiled. Scheuring and Sturgis show that the organization of membrane proteins is not fixed but can vary with membrane location and time. This work was published in the July 15, 2005 issue of Science.

The body’s innumerable cells with their specialized tasks contain organelles, which perform particular functions. If they are to operate efficiently in the right location, organelles and cells alike must be suitably differentiated and above all isolated. This is the role of the lipid bilayers that constitute membranes.



But membranes are not simple barriers, they also act as border guards, assisted by membrane proteins which oversee the comings and goings between the cell and the outside world. Membranes also relay information across the cellular divide and so are essential for communication between cells and their environment. Informative messages from outside the cell (other cells, tissues and organs) are received by membrane receptors, which activate proteins within the cell, which in turn activate other proteins, and so forth, until there is a genetic response. Once decoded, these signals enable cells to determine their position and role within the body. The signals are essential for the proliferation, differentiation, morphology and mobility of cells and for key cellular functions. These signals ensure that the size and function of organ tissues are maintained harmoniously.

Nearly 70% of drugs target membrane proteins(1)

Observing protein supercomplexes

Membrane proteins generally do not operate in isolation but instead combine to form protein supercomplexes. One of the best known complexes transforms light energy into ATP(2) in photosynthetic bacteria such as Rhodospirillum photometricum (see box). Atomic data on these various membrane components are relatively abundant, but until now information on the organization of these complexes has been scarce because we have lacked suitable tools.

Exploring the depths of the cell by atomic force microscopy

Simon Scheuring and James N. Sturgis have recorded high-resolution images of biological membranes under physiological conditions using atomic force microscopy, a technique developed by physicists in 1986, which provides atomic resolution images of a sample’s surface. An atomically sharp tip is scanned over the sample surface and its movements are tracked by a laser. The resulting data can be used to draw a topographical map of the sample.

Atomic force microscopy has the enormous advantage of being able to analyze samples in solution, which is a major asset for biology. Since 1995, membrane proteins have been studied by atomic force microscopy at a lateral resolution of 10 Angstroms and vertical resolution of 1 Angstrom (one ten thousand millionth of a meter). This has now defined the contours of many membrane proteins that work together in native membranes – i.e. membranes close to their natural state – thereby revealing their organization.

In photosynthetic bacteria, membrane organization changes with the intensity of incident light. In dim light, the proportion of light-harvesting complexes is higher. The reaction centers “manage” the harvested light and minimize losses. Lost light may induce the formation of free radicals that damage DNA and proteins and the bacterium itself in the longer term.

Membranes respond to the environment and adapt their organization as required. These results confirm that membranes are not homogeneous: a given membrane has several possible compositions (variable position and quantity of lipids and membrane proteins). Researchers have used this example to study general aspects of membrane organization.

In addition to enhancing our understanding of photosynthesis in bacteria, these findings amply demonstrate the value of atomic force microscopy in observing proteins in native membranes on the nanometer scale (i.e. one millionth of a millimeter). Simon Scheuring penetrates the depths of these protein complexes by observing them in situ and under physiological conditions.

Cells will progressively yield up their secrets as they are explored using a combination of high-resolution imaging, as in atomic force microscopy, optical microscopy and electron microscopy.

Catherine Goupillon | alfa
Further information:
http://www.sciencemag.org/
http://www.curie.fr

More articles from Life Sciences:

nachricht Ion treatments for cardiac arrhythmia — Non-invasive alternative to catheter-based surgery
20.01.2017 | GSI Helmholtzzentrum für Schwerionenforschung GmbH

nachricht Seeking structure with metagenome sequences
20.01.2017 | DOE/Joint Genome Institute

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Traffic jam in empty space

New success for Konstanz physicists in studying the quantum vacuum

An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...

Im Focus: How gut bacteria can make us ill

HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host

Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Sustainable Water use in Agriculture in Eastern Europe and Central Asia

19.01.2017 | Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

 
Latest News

Helmholtz International Fellow Award for Sarah Amalia Teichmann

20.01.2017 | Awards Funding

An innovative high-performance material: biofibers made from green lacewing silk

20.01.2017 | Materials Sciences

Ion treatments for cardiac arrhythmia — Non-invasive alternative to catheter-based surgery

20.01.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>