Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Zooming in on the protein-conducting channel

17.11.2005


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 native structure. Using an electron microscope with a low-intensity beam to avoid damaging the molecules, scientists then obtained images of thousands of captive protein complexes. Next, they used computer image analysis to produce detailed, three-dimensional maps of the complex in two different states from the low-contrast, noisy images produced by the electron microscope.

“What we have achieved is a huge jump in resolution of this complex,” said Frank. “Even so, this resolution would not allow us to study the complex in atomic detail, or even see individual helices.” He said the results from the cryo-EM analysis were informed by detailed x-ray crystallographic data on the PCC structure done by other researchers. In x-ray crystallography, an x-ray beam is directed through crystals of a target protein. As the x-rays pass through the crystal, they are diffracted. Researchers can then analyze the diffraction pattern to determine the atomic structure of the protein.

The analysis by Frank and his colleagues revealed that each channel consists of two PCC subunits joined in a clamshell arrangement. The cryo-EM data also revealed two different arrangements of the PCC -- one that was apparently in the functional, or “translocating” state, and one in a non-translocating state.

X-ray crystallography data from the lab of HHMI investigator Tom A. Rappaport suggested that the halves of the PCC clamshell were joined in a back-to-back arrangement. However, said Frank, x-ray crystallographic structures often do not represent the arrangements of proteins in their native functional state.

Thus, he and his colleagues applied a computational analytical method called “normal mode-based flexible fitting” (NMFF) to model how well the two possible channel structures could explain the structural data from cryo-EM. The NMFF method was developed and applied by co-authors Florence Tama and Charles Brooks of the Scripps Research Institute. The technique provides dynamic information on the multitude of vibrations and motions that complex molecules preferentially undergo.

NMFF analysis revealed that the cryo-EM data were best explained by a model in which the two PCC clamshells were joined in a “front-to-front” arrangement. This arrangement yielded significant insight into how the channel functions to translocate proteins across or into membranes, said Frank.

“Now that we have these new insights into the architecture of the PCC in its translocating, and possibly non-translocating state, we can explore the mechanisms of perpendicular versus lateral transport,” Frank said.

Jennifer Michalowski | EurekAlert!
Further information:
http://www.hhmi.org

More articles from Life Sciences:

nachricht Nanoparticle Exposure Can Awaken Dormant Viruses in the Lungs
16.01.2017 | Helmholtz Zentrum München - Deutsches Forschungszentrum für Gesundheit und Umwelt

nachricht Cholera bacteria infect more effectively with a simple twist of shape
13.01.2017 | Princeton University

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

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...

Im Focus: How to inflate a hardened concrete shell with a weight of 80 t

At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).

Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...

Im Focus: Bacterial Pac Man molecule snaps at sugar

Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.

The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...

Im Focus: Newly proposed reference datasets improve weather satellite data quality

UMD, NOAA collaboration demonstrates suitability of in-orbit datasets for weather satellite calibration

"Traffic and weather, together on the hour!" blasts your local radio station, while your smartphone knows the weather halfway across the world. A network of...

Im Focus: Repairing defects in fiber-reinforced plastics more efficiently

Fiber-reinforced plastics (FRP) are frequently used in the aeronautic and automobile industry. However, the repair of workpieces made of these composite materials is often less profitable than exchanging the part. In order to increase the lifetime of FRP parts and to make them more eco-efficient, the Laser Zentrum Hannover e.V. (LZH) and the Apodius GmbH want to combine a new measuring device for fiber layer orientation with an innovative laser-based repair process.

Defects in FRP pieces may be production or operation-related. Whether or not repair is cost-effective depends on the geometry of the defective area, the tools...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

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

Nothing will happen without batteries making it happen!

05.01.2017 | Event News

 
Latest News

Multiregional brain on a chip

16.01.2017 | Power and Electrical Engineering

New technology enables 5-D imaging in live animals, humans

16.01.2017 | Information Technology

Researchers develop environmentally friendly soy air filter

16.01.2017 | Power and Electrical Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>