Scientists map the entire active protein inventory in cells

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Scientists map the entire active protein inventory in cells

http://www.news-medical.net/?id=18154

Working with colleagues from Denmark, Canada, China, and the U.S.A.,

the scientists have shown how cutting-edge methods can be used to

catalogue the entire inventory of active proteins in cell organelles

at a particular moment. Their work sheds considerable light on how

cells use proteins. The work is published in the journal Cell.

Cells are like small cities. They contain all the necessary parts

that allow their infrastructure, function, growth, and communication

to operate. For over a century scientists have been looking at the

structures and organelles in cells using microscopic methods, and

then drawing conclusions about their function. Biochemical methods

have allowed scientists to examine the inner life of the cell, an

organisational unit basic to all life. Now, they are clarifying its

structures in detail: from mitochondria, the " factories " of cells,

which create energy; to the endoplasmic reticulum, necessary for

protein synthesis and metabolic processes; to the Golgi apparatus,

responsible for lipid synthesis and producing important energy

reserves for cell growth.

Now scientists led by Matthias Mann have specialised in identifying

individual proteins in protein complexes. Proteins have various

functions in a cell, from transport to mechanical support. As

enzymes, they catalyse all kinds of metabolic processes. They are

also important components of signal chains, like those which transmit

information from the exterior of the cell to its nucleus. In this

way, proteins also control the transcription of genetic information

and the synthesis of new proteins that comes with it.

In this study, the proteome researchers looked at liver cells in

mice. Using mass spectrometry, and by comparing databases, the

scientists were able to detect more than 1400 proteins, localised in

ten different cell compartments. Previous analyses had shown that

certain proteins assign themselves clearly to particular cell

organelles. When the scientists took the protein complex apart, these

proteins were used as markers. Proteins which appear together with

these marker-proteins could now also be assigned their proper place

in the inventory. This method, called protein correlation profiling,

was developed by Matthias Mann and his colleagues, and has previously

been successfully used to determine the composition of single cell-

organelle protein.

After the individual " compartments " for the proteins were identified,

the scientists compared corresponding protein sets of individual cell

organelles. Among the 1400 different proteins that can be clearly

mapped onto individual cell organs, around 40% of them also appear in

other cell organs. This result can be compared with studies on yeast

cells. Their proteins have stayed " true " to their cell organelles

over the course of evolution. Their localisation has apparently

remained stable over almost a billion years, as simple organisms

evolved all the way to mammals.

These results are a milestone in cell biology. Matthias Mann

says, " for the first time, we are able to determine where exactly in

the cell large numbers of proteins belong. It allows a new

understanding of their function and interaction with other cellular

proteins and cell organelles. " The researchers hope that protein

correlation profiling will allow them to determine which proteins

participate in failures of regulation. This could contribute to

research into diseases which occur when communication between cells

is disturbed.

http://www.mpg.de