Cell membrane is patterned like a patchwork quilt

May 05, 2012
Cell membrane is patterned like a patchwork quilt
The membrane of the yeast cell is divided into different domains (highlighted in colour), giving it the appearance of a molecular patchwork quilt. © MPI f. Biochemistry/Wedlich-Söldner

(Phys.org) -- As the interface between the cell and its environment, the cell membrane, which consists of fats and proteins, fulfils a variety of vital functions. Scientists at the Max Planck Institute of Biochemistry in Martinsried near Munich have performed the first comprehensive analysis of the molecular structure of this boundary layer, and revealed precisely how it is organised. In yeast cells, the entire membrane is made up of independent domains, each containing just one or a few protein types. If a protein is relocated to an inappropriate domain, it may even fail to function. The study shows that the membrane is a kind of patchwork quilt and should help scientists to gain a better understanding of basic cellular processes.

The must process numerous signals from the environment and the cell interior in order to initiate apposite molecular responses to changing conditions. For example, if certain messenger substances bind to the membrane, this can trigger the growth or division of a cell. The cell membrane has long been the focus of scientific research. One aspect that has remained largely unexplained, however, is exactly how its various components organise themselves. According to an early model, the fats (lipids) and proteins anchored in the membrane are in constant flux and do not form fixed structures. That at least some are organised in bounded domains was only proven quite recently, and only for a small number of proteins.

Researchers working with Roland Wedlich-Söldner, a group leader at the Max Planck Institute of Biochemistry, have now carried out the first comprehensive analysis of the of the cell membrane. They used advanced imaging technologies for the purpose, enabling them to obtain much sharper images of the cell membrane and the marked proteins within them than were previously available. They discovered that domain formation in the cell membrane is not the exception, but the rule. Each protein in the cell membrane is located in distinct areas that adopt a patch- or network-like structure. The entire cell membrane thus consists of domains – like a kind of molecular patchwork quilt.

“Some areas contain more than one type of protein,” says Roland Wedlich-Söldner. “Even if these molecules fulfil entirely different functions, they generally have one thing in common: they are attached to a shared domain in the membrane by a similar or identical molecular anchor.” In another experiment, the scientists succeeded in demonstrating the extent to which the protein function depends on this specific environment: they replaced the original anchor in some proteins with another molecular variant. The modified proteins then relocated to a “foreign” domain that matched the new anchor. However, they were no able longer to function correctly in their new surroundings.

How then do proteins find the appropriate domain and remain associated with it, despite being relatively mobile in the plane of the membrane? The researchers were able to show that the lipids in the cell membrane play a central role in this process. Different lipids prefer to accumulate around certain protein anchors. Therefore, areas arise that are particularly attractive to proteins with a similar type of anchor. This could explain how cell membranes self-organise – another previously unanswered question in biology. The highly ordered structure of the cell membrane could help scientists to gain a better understanding of its many functions. “One may assume that many processes only function efficiently thanks to the formation of domains in the cell membrane,” says Wedlich-Söldner. “It is possible that the cell exploits a principle that also applies in everyday life: a certain degree of order makes it much easier to get things done.”

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kevinrtrs
1.2 / 5 (5) May 06, 2012
Though it's heartening to see that there is no evolutiontary fairytale attached to this research report, it is nevetheless clear that the researchers still rely on the assumption that the cell somehow spontaneously arises and organises itself.
One of the major problems that now arises is the fact that the cell membrane is organised into domains instead of having proteins and lipids mixed in at random. This is a particular problem for any notion that the cell could have somehow arisen by spontaneous self-assembly. The more the researchers reveal, the more difficult it gets to escape the strongest indications that life had to have been created by an outside intellegent agent. Only by blindly ignoring the facts in front of you and going purely on philosophical dogma, can one come to the conclusion that life arose spontaneously from nothing more than raw physical and chemical processes.I need to point out that right now there is zero true scientific support for such spontaneous life start.
FieryJack
5 / 5 (3) May 06, 2012
kevintrs, it may surprise you to know that mixtures of lipids (fats) such as those in the cell membrane form domains on thier own, simply due to physical forces. The trick evolution has brought is to generate proteins, which can make use of this natural segregation for compartmentalization of processes.
Irukanji
not rated yet May 07, 2012
Adding to FieryJack's comment, proteins will only couple with other proteins in a specific way. Therefore, once all the respective proteins have came into existence, it was only a matter of time before they hooked up. And since amino acids are the backbone of proteins, after any given amount of time and provided the right energy, they will form into proteins and in turn into cell walls which can then be used to start life. And given the fact there are several hundred trillion stars, the likelihood of life becomes high, as is the case with earth.

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