For most proteins, there is a particular place inside a cell where they carry out their function. But how do they get there? Scientists from the Charité Berlin, the University of Heidelberg, and the Max Planck Institute for Molecular Genetics in Berlin have now been able to visualize the structure of a "molecular machine" involved in protein sorting using cryo-electron microscopy and single particle analysis. This "machine" is made up of a single active ribosome, plus a special signal recognition protein and a matching receptor. The scientists have shown that when the three proteins interact, certain areas open up on the ribosome, which allows the ribosome to dock onto another complex. The later complex, which is called translocon complex, takes over the job of transferring a newly produced protein through the membrane. Knowing the structure of the molecular machine helps scientists to understand how secretory and membrane proteins in a cell are expressed and sorted (Science, May 5, 2006).

Sorting proteins is fundamental to the gene expression of every organism - from bacteria to humans. Particularly important during biosynthesis is sorting secretory and membrane proteins, which have to find the way to their final destination inside or outside the cell. Secretory proteins are those that later on leave the cell, like anti-bodies. Membrane proteins are proteins embedded into the cell's membranes - for example, signalling receptors. One particular molecular complex is important in protein sorting. It is made from an active ribosome - that is, the protein synthesis machine in the cell - called the signal recognition particle (SRP), and its corresponding receptor. It is the structure of this complex that the scientific team is now able to describe.

The key element to this machine's functioning is a signal sequence located at the N-terminal end of the protein to be sorted. The sequence acts as a kind of "postal code" in the cell. The SRP reads the sequenc
'"/>

Contact: Dr. Thorsten Mielke
mielke@molgen.mpg.de
Max-Planck-Gesellschaft
12-May-2006

Page: 1 2
Related biology news :

1. New textbook illuminates the close links between evolutionary and molecular biology
2. New molecular regulators of hyperthyroidism and goiter
3. A novel molecular dictator with a conscience discovered
4. UC Santa Barbara scientists clarify molecular basis of interferon action
5. MU researchers make discovery in molecular mechanics of phototropism
6. Malaria-resistant mosquitoes battle disease with molecular warhead
7. University of Cincinnati receives $1.7M to research molecular treatment of brain injury
8. Casting the molecular net
9. Tumor vessels identified by unique molecular markers
10. SNM advances professional definition for molecular imaging
11. Uncovering the molecular basis of obesity