Featured Research

from universities, journals, and other organizations

Protein structure: Peering into the transit pore

Date:
February 7, 2014
Source:
Ludwig-Maximilians-Universitaet Muenchen (LMU)
Summary:
The lipid-rich membranes of cells are largely impermeable to proteins, but evolution has provided a way through -- in the form of transmembrane tunnels. A new study shows in unmatched detail what happens as proteins pass through such a pore.

Every cell is surrounded by a surface membrane and contains internal compartments bounded by membranes. Almost one-third of all proteins synthesized in cells must pass through these membranes or be incorporated into them in order to fulfill their functions.
Credit: Image courtesy of Ludwig-Maximilians-Universitaet Muenchen

The lipid-rich membranes of cells are largely impermeable to proteins, but evolution has provided a way through -- in the form of transmembrane tunnels. A new study shows in unmatched detail what happens as proteins pass through such a pore.

Every cell is surrounded by a surface membrane and contains internal compartments bounded by membranes. Almost one-third of all proteins synthesized in cells must pass through these membranes or be incorporated into them in order to fulfil their functions. However, the fat-rich nature of membranes makes it impossible for most proteins to percolate through them directly. Therefore, biological membranes contain so-called protein-conducting channels, molecular pores through which proteins can pass.

"Structural investigations have already provided clues to how proteins are inserted into the membrane and then drawn through it like a length of thread to emerge on the other side," says Professor Roland Beckmann of the Gene Center of Ludwig-Maximilians-Universitaet (LMU) in Munich. "However, conclusive proof for these mechanisms has been lacking until now."Protein-conducting channels are known to be shaped like an hour-glass, consisting of two cones connected by a narrow central constriction. In the inactive form, the constriction is blocked by a plug that protrudes from the side-wall. Presumably, if a protein is to cross the membrane, the channel must be opened to provide a continuous aqueous environment for its passage. If, on the other hand, a protein is to be inserted within the membrane itself, it must emerge from a lateral opening within the tunnel.

Imaging the crucial transition

"Up until now, it had not been possible to characterize these structural transitions with the required spatial and temporal resolution," Beckmann says. Now he and his colleagues have, for the first time, succeeded in isolating transitional forms of the active channel, and elucidating their three-dimensional structures with the help of cryo-electron microscopy -- at the unprecedented resolution of less than 1 nanometer. "This allowed us to determine the spatial conformations of the individual protein strands that make up the channel and to analyze how the channel behaves during its functional cycle," he explains.

Indeed, the researchers were even able to capture a snapshot of the complex at the moment when a protein leaves the channel to be incorporated into the cell membrane. "It turns out that there actually is a side-door within the channel, which opens to allow the protein to diffuse into the membrane," Beckmann says. Interestingly, as the lateral gate opens and the protein exits the channel into the membrane, the plug moves into the central constriction, blocking access to the outside and preventing diffusion of ions through the now empty channel. Surprisingly, proteins destined to cross the membrane do so without altering the position of the plug very much. Instead, an adjacent strand shifts slightly outward, widening the constriction sufficiently to let the protein through the length of the tunnel.

Beckmann and his team now hope to be able to increase the resolution of their snapshots still further. "Our goal is to achieve a resolution of less than 0.4 nm, in order to discern the interactions in molecular detail and understand the dynamic changes that take place in the structure of the channel," he says. In addition, the scientists want to image other membrane protein complexes -- such as visual pigments -- and analyze how a single chain of amino acids can function as a dynamically active membrane receptor.


Story Source:

The above story is based on materials provided by Ludwig-Maximilians-Universitaet Muenchen (LMU). Note: Materials may be edited for content and length.


Journal Reference:

  1. Marko Gogala, Thomas Becker, Birgitta Beatrix, Jean-Paul Armache, Clara Barrio-Garcia, Otto Berninghausen, Roland Beckmann. Structures of the Sec61 complex engaged in nascent peptide translocation or membrane insertion. Nature, 2014; 506 (7486): 107 DOI: 10.1038/nature12950

Cite This Page:

Ludwig-Maximilians-Universitaet Muenchen (LMU). "Protein structure: Peering into the transit pore." ScienceDaily. ScienceDaily, 7 February 2014. <www.sciencedaily.com/releases/2014/02/140207083730.htm>.
Ludwig-Maximilians-Universitaet Muenchen (LMU). (2014, February 7). Protein structure: Peering into the transit pore. ScienceDaily. Retrieved October 21, 2014 from www.sciencedaily.com/releases/2014/02/140207083730.htm
Ludwig-Maximilians-Universitaet Muenchen (LMU). "Protein structure: Peering into the transit pore." ScienceDaily. www.sciencedaily.com/releases/2014/02/140207083730.htm (accessed October 21, 2014).

Share This



More Plants & Animals News

Tuesday, October 21, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

White Lion Cubs Born in Belgrade Zoo

White Lion Cubs Born in Belgrade Zoo

AFP (Oct. 20, 2014) Two white lion cubs, an extremely rare subspecies of the African lion, were recently born at Belgrade Zoo. They are being bottle fed by zoo keepers after they were rejected by their mother after birth. Duration: 00:42 Video provided by AFP
Powered by NewsLook.com
Traditional Farming Methods Gaining Ground in Mali

Traditional Farming Methods Gaining Ground in Mali

AFP (Oct. 20, 2014) He is leading a one man agricultural revolution in Mali - Oumar Diatabe uses traditional farming methods to get the most out of his land and is teaching others across the country how to do the same. Duration: 01:44 Video provided by AFP
Powered by NewsLook.com
Goliath Spider Will Give You Nightmares

Goliath Spider Will Give You Nightmares

Buzz60 (Oct. 20, 2014) An entomologist stumbled upon a South American Goliath Birdeater. With a name like that, you know it's a terrifying creepy crawler. Sean Dowling (@SeanDowlingTV) has the details. Video provided by Buzz60
Powered by NewsLook.com
Adorable Video of Baby Rhino and Lamb Friend Playing

Adorable Video of Baby Rhino and Lamb Friend Playing

Buzz60 (Oct. 20, 2014) Gertjie the Rhino and Lammie the Lamb are teaching the world about animal conservation and friendship. TC Newman (@PurpleTCNewman) has the adorable video! Video provided by Buzz60
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins