Featured Research

from universities, journals, and other organizations

Under The Hood Of A Cellular Transport Machine

Date:
June 23, 1999
Source:
Harvard Medical School
Summary:
A collaboration between researchers in Great Britain, Italy, and Harvard has developed a newly detailed view of one of the cell's major transport vehicles responsible for shuttling into the cell a range of important molecules, including cholesterol.

Collaboration sheds light on assembly of transporter associated with cholesterol, breast cancer, and HIV

Related Articles


Boston, MA (June 12, 1999) -- A collaboration between researchers in Great Britain, Italy, and Harvard has developed a newly detailed view of one of the cell's major transport vehicles responsible for shuttling into the cell a range of important molecules, including cholesterol.

The findings, presented in the June Molecular Cell, provide insight into how this machine, the clathrin-coated vesicle, is formed, stays together, and falls apart.

A video of the clathrin protein can be viewed on the Web at www.hms.harvard.edu/news/clathrin/. Clathrin-coated vesicles are constantly assembling and disassembling to perform their task of transporting proteins from the outside of the cell inside. They are responsible for importing LDL cholesterol, and they play a role in breast cancer through internalization of a key receptor.

During disease progression of HIV infection, clathrin-coated vesicles are subverted by a viral protein to cause down-regulation of the viral receptor CD4 in an important but not fully understood step. These molecules, and a wide range of others, are selectively trapped in the clathrin-coated vesicle for import into the cell.

The new insights into how the vesicle forms help build a picture of the overall process and suggest possible targets for future therapeutic intervention.

One mystery of clathrin vesicles is how the outer cage of clathrin assembles so rapidly. Vesicles are incessantly assembled and disassembled at an incredible scale. In the brain, where neurotransmitters are constantly released into synapses, the membrane used to export the neurotransmitters is constantly being dragged back in by clathrin-coated vesicles.

"The equivalent of the entire brain, or a football field of membrane, is turned over every hour," says Tomas Kirchausen, associate professor of cell biology at the Center for Blood Research and Harvard Medical School and senior author on the article last year describing clathrin's atomic structure.

The new work allows Kirchhausen and colleagues to propose that clathrin molecules add to the growing cage lattice by hooking into spaces in the existing structure, then rapidly rotating into a locked position. The process is reminiscent of images of alien space ships locking into the mother vessel (see video).

The new insights come from combining an overall view of a barrel-shaped clathrin lattice, obtained using cryo-electron microscopy by Barbara Pearse and colleagues at the MRC Laboratory for Molecular Biology in England, with the much more detailed view of a portion of the protein derived from X-ray crystallography by Tomas Kirchhausen, Stephen Harrison, and colleagues at Harvard Medical School, the Center for Blood Research, Children's Hospital and the Howard Hughes Medical Institute, and Andrea Musacchio, now at the European Institute of Oncology in Milan, Italy.

Both sets of data were published late last year, but by collaborating to combine them the researchers managed to identify the portions of the clathrin molecule that flex during the assembly of the lattice.

A single clathrin molecule is made up of three clathrin heavy chains combined at a hub to make a three-legged pinwheel, a triskelion. Each leg has a "knee" where the molecule bends and a "foot" that interacts with adapter proteins to form the lattice.

To bring something from the outside of the cell inside, clathrin molecules combine at the cell membrane to form a clathrin-coated pit on the inside surface of the outer cell membrane. The pit then rounds and pinches off, trapping a section of membrane in a clathrin-coated vesicle. The membrane section, and the associated receptor proteins, are then carried into the cell for processing, disassembly, or recycling.

In a growing lattice, each newly added molecule must fit precisely into the tight space of the pre-existing structure to make the hexagons and pentagons that form a cage. The whole process, with a minimum of 36 triskelions fitting together to make a geometrically perfect arrangement, must take place in less than a minute (pentagons are required to make a closed structure, since an array of hexagons would be a flat sheet).

The researchers find that most of the clathrin molecule is rigid, with the only flexibility occurring at the knee, where twisting and bending is allowed. This flexibility is what enables the same molecule to form both hexagons and pentagons. The feet, which capture the cargo molecules and select them for inclusion in the vesicle, project into the center of the cage to contact the cell membrane. Receptor protein binding sites are on these feet, perfectly placed to interact with receptors bound in the membrane.

###

Andrea Musacchio co-first author of this paper was a fellow at the Armenise Center for Structural Biology at Harvard Medical School, one of four centers established by the Giovanni Armenise-Harvard Foundation beginning in 1996. Established through the support of Count Auletta Armenise, in honor of his uncle, the foundation funds basic research at HMS in neurobiology, cell signal transduction, human cancer viruses, and structural biology and fosters exchange between Italian and American scientists. Andrea Musacchio is currently establishing a new center for Structural Biology at the European Institute of Oncology in Milan, Italy in part with funding from the Armenise-Harvard Foundation.

Editors, please note: A video of the clathrin protein is available at /www.hms.harvard.edu/news/clathrin/.


Story Source:

The above story is based on materials provided by Harvard Medical School. Note: Materials may be edited for content and length.


Cite This Page:

Harvard Medical School. "Under The Hood Of A Cellular Transport Machine." ScienceDaily. ScienceDaily, 23 June 1999. <www.sciencedaily.com/releases/1999/06/990623062321.htm>.
Harvard Medical School. (1999, June 23). Under The Hood Of A Cellular Transport Machine. ScienceDaily. Retrieved December 19, 2014 from www.sciencedaily.com/releases/1999/06/990623062321.htm
Harvard Medical School. "Under The Hood Of A Cellular Transport Machine." ScienceDaily. www.sciencedaily.com/releases/1999/06/990623062321.htm (accessed December 19, 2014).

Share This


More From ScienceDaily



More Health & Medicine News

Friday, December 19, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

The Best Tips to Curb Holiday Carbs

The Best Tips to Curb Holiday Carbs

Buzz60 (Dec. 19, 2014) — It's hard to resist those delicious but fattening carbs we all crave during the winter months, but there are some ways to stay satisfied without consuming the extra calories. Vanessa Freeman (@VanessaFreeTV) has the details. Video provided by Buzz60
Powered by NewsLook.com
Sierra Leone Bikers Spread the Message to Fight Ebola

Sierra Leone Bikers Spread the Message to Fight Ebola

AFP (Dec. 19, 2014) — More than 100 motorcyclists hit the road to spread awareness messages about Ebola. Nearly 7,000 people have now died from the virus, almost all of them in west Africa, according to the World Health Organization. Video provided by AFP
Powered by NewsLook.com
Researchers Test Colombian Village With High Alzheimer's Rates

Researchers Test Colombian Village With High Alzheimer's Rates

AFP (Dec. 19, 2014) — In Yarumal, a village in N. Colombia, Alzheimer's has ravaged a disproportionately large number of families. A genetic "curse" that may pave the way for research on how to treat the disease that claims a new victim every four seconds. Duration: 02:42 Video provided by AFP
Powered by NewsLook.com
Double-Amputee Becomes First To Move Two Prosthetic Arms With His Mind

Double-Amputee Becomes First To Move Two Prosthetic Arms With His Mind

Buzz60 (Dec. 19, 2014) — A double-amputee makes history by becoming the first person to wear and operate two prosthetic arms using only his mind. Jen Markham has the story. 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

 

Health & Medicine

Mind & Brain

Living & Well

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