Researchers have gained the most detailed view yet of the heart of the translocon, a channel through which newly constructed proteins are inserted into the cell membrane. The process of transporting proteins across or into membranes is a critical function that occurs in every cell.
Howard Hughes Medical Institute investigator Joachim Frank at the Wadsworth Center and his colleagues reported their detailed study of the translocon's core, called the protein-conducting channel (PCC), in an article published in the November 17, 2005, issue of the journal Nature. Co-lead authors on the paper were Kakoli Mitra in Frank's laboratory and Christiane Schaffitzel of the Eidgenössische Technische Hochschule Hönggerberg in Switzerland, who is in the laboratory of the other senior author, Nenad Ban. Other co-authors were from the Scripps Research Institute and the State University of New York at Albany.
The researchers studied the PCC, which grabs newly made protein as it is extruded from the ribosome's protein synthesis machinery. The PCC then opens either a pore that is perpendicular or lateral to the cell membrane to feed the new protein either across or into the membrane.
For the studies, the Swiss researchers created a complex comprising the PCC from E. coli attached to a ribosome that contained a newly forming protein segment. The ribosome is the massive protein-RNA complex that constitutes the cell's protein-making machinery.
Mitra explored the structure of this PCC-ribosome complex using three-dimensional cryogenic electron microscopy (cryo-EM), as well as computational methods. Three-dimensional cryo-EM is one of the few techniques capable of visualizing large, dynamic molecules.
In preparing for cryo-EM, researchers immersed the PCC-containing complex in water and then abruptly froze it in supercold liquid ethane. The rapid freezing imprisoned the complex in vitreous ice, a glassy non-crystalline form of ice, thus preserving its na
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Source:HHMI
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