Navigation Links
Caltech scientists get detailed glimpse of chemoreceptor architecture in bacterial cells

PASADENA, Calif.Using state-of-the-art electron microscopy techniques, a team led by researchers from Caltech has for the first time visualized and described the precise arrangement of chemoreceptorsthe receptors that sense and respond to chemical stimuliin bacteria. In addition, they have found that this specific architecture is the same throughout a wide variety of bacterial species, which means that this is a stable, universal structure that has been conserved over evolutionary time.

Their research, which was published this week in the online early edition of the Proceedings of the National Academy of Sciences (PNAS), may help scientists better understand the complex signaling pathways that are at the core of many biological processes.

Bacteria swim using flagella to propel themselves. But it's not as simple as that, explains Grant Jensen, associate professor of biology at Caltech and an investigator with the Howard Hughes Medical Institute (HHMI), who led the team. After all, they need to decide where to swim. "They tend to swim toward a favorable environment, and away from a harsh environment," Jensen says.

How do they know which is which? Enter the chemoreceptors, tiny protein molecules found at the front of the bacterium, near the flagella. "It's like a protein antenna that protrudes from the bacterial cell body, through the membrane, and out onto the surface," says Jensen. "It binds to nutrients and other chemical stimuli."

While swimming in a single direction, a bacterium such as Escherichia coli may encounter some nutrients, which then bind to the chemoreceptors. "This transmits a signal to the inside of the cell saying that things are good," says Jensen. "So the bacterium will keep swimming in the same direction. But if there are no good nutrients, the cell will do something called 'tumbling,' in which it stops and randomly flips over in the fluid, then starts swimming again in a random direction in a search for better conditions."

"One of the remarkable things about this system," says Jensen, "is that the chemoreceptors are exquisitely sensitive to changes in the concentrations of positive and negative stimuli."

Scientists believe that this sensitivity is due to the way the hundreds of chemoreceptors cluster together in the bacterial cell. "It is known that if one receptor binds a stimulus molecule, it turns on other receptors around it as well to amplify the signal," Jensen explains. "The whole system also adapts to changing conditions, dynamically adjusting the range of concentrations that it responds to."

To fully understand just what is happening in these cells, Jensen says, it is thus important to figure out the ways in which these receptors interact with one another, which in turn depends on understanding precisely how they are situated in relation to one another.

In other words, scientists need to be able to "see" the internal architecture of the bacterial cell and, in particular, how its chemoreceptors are arrayed.

Jensen and his team were able to get just such a glimpse at the chemoreceptor architecture at the macromolecular level, thanks to a state-of-the-art electron cryomicroscope that was purchased with a gift from the Gordon and Betty Moore Foundation.

"The electron cryomicroscope allows us to see the arrangement of individual proteins inside cells in a lifelike state," says Jensen. "To do this, living cells are quickly frozen so that all the proteins are frozen in placein the same places they were in the living state."

The high-tech microscope allowed the researchers to take 3-D images of intact cells through a technique called electron cryotomography. The researchers looked at some 700 tomographic imagesor tomogramsof bacterial cells, says Caltech postdoctoral scholar Ariane Briegel, the first author on the PNAS paper, and an HHMI associate. "This is the first time such a large number of tomograms was used to answer a biological question," she notes. "And it was made possible by the combination of a state-of-the-art electron microscope and fully automated data collection."

What they saw when they glimpsed the insides of these quick-frozen bacteria were chemoreceptors arranged in a regular, repeating lattice of hexagonsa structure with six sides and six corners or verticesthat are 12 nanometers apart, center to center. At each of the vertices sit six chemoreceptors, arranged in what scientists call "trimers of dimers," which means there are three sets of two paired receptors in each grouping. The two receptors in each dimer twine around one another, and those dimers then cluster together at one vertex of the hexagon to form a trimer.

"One beauty of this is that we've shown that the receptors cluster in cells in the same way they did in the crystal structure," says Jensen. "In the past, we didn't know if that was an artifact of the crystallography. Now we can see how the pieces fit together in real cells."

The paper also showed that this particular architecture is no single-species fluke. "We looked at 13 different species that cover the whole bacterial kingdom," Jensen says. "The arrays were all the same. This shows us that this structure has been universally conserved, that it's a universal architecture."

And that's important to know, he adds, because it gives scientists a basis for trying to figure out how this sort of architecture leads to the bacteria's sensitivity to chemical cues in its environment and establishes that work using key model systems such as E. coli will be generally applicable.

"Bacterial chemotaxis consists of only a few key components, making it an important model system for all cell signaling pathways," says Briegel. "We need to understand this system first before we can hope to fully understand the more complex eukaryotic signaling systems. Chemotaxis also plays an important role in the first steps of host invasion for pathogenic bacteria. Understanding it might help in the development of new antimicrobial agents."


Contact: Lori Oliwenstein
California Institute of Technology

Related biology news :

1. Caltech neuroscientists find brain region responsible for our sense of personal space
2. Caltech researchers explore how cells reconcile mixed messages in decisions about growth
3. Caltech scientists reveal how neuronal activity is timed in brains memory-making circuits
4. Caltech scientists show why anti-HIV antibodies are ineffective at blocking infection
5. Caltech scientists control complex nucleation processes using DNA origami seeds
6. Caltech researchers train computers to analyze fruit-fly behavior
7. Caltech and UCSD researchers shed light on how proteins find their shapes
8. Caltech researchers help unlock the secrets of gene regulatory networks
9. Caltech researchers get first look at how groups of cells coordinate their movements
10. Caltech scientists show function of helical band in heart
11. Caltech scientists develop barcode chip for cheap, fast blood tests
Post Your Comments:
Related Image:
Caltech scientists get detailed glimpse of chemoreceptor architecture in bacterial cells
(Date:11/17/2015)... -- Vigilant Solutions announces today that Mr. Dick W. ... --> --> Mr. Boyce ... at TPG Capital, one of the largest global investment ... revenue.  He founded and led TPG,s Operating Group, which ... 1997 to 2013.  In his first role, he served ...
(Date:11/12/2015)...  Arxspan has entered into an agreement with ... use of its ArxLab cloud-based suite of biological ... will support the institute,s efforts to electronically manage ... internally and with external collaborators. The ArxLab suite ... Institute,s electronic laboratory notebook, compound and assay registration, ...
(Date:11/10/2015)... YORK , Nov. 10, 2015 ... to behavioral biometrics that helps to identify and ... fraud. Signature is considered as the secure and ... the identification of a particular individual because each ... more accurate results especially when dynamic signature of ...
Breaking Biology News(10 mins):
(Date:11/24/2015)... , Nov. 24, 2015 Cepheid (NASDAQ: ... be speaking at the following conference, and invited investors ... York, NY      Tuesday, December 1, 2015 at ... York, NY      Tuesday, December 1, 2015 at ... Healthcare Conference, New York, NY ...
(Date:11/24/2015)... ... November 24, 2015 , ... ... the year and one of the premier annual events for pharmaceutical manufacturing: 2015 ... 8–11 November 2015, where ISPE hosted the largest number of attendees in more ...
(Date:11/24/2015)... ... 2015 , ... This fall, global software solutions leader SAP and AdVenture Capital ... and pitch their BIG ideas to improve health and wellness in their schools. , ... win the title of SAP's Teen Innovator, an all-expenses paid trip to Super Bowl ...
(Date:11/24/2015)... 24, 2015  Tikcro Technologies Ltd. (OTCQB: TIKRF) today announced that its ... at 11:00 a.m. Israel time, at the law ... Allon Street, 36 th Floor, Tel Aviv, Israel ... and Izhak Tamir to the Board of Directors; ... directors; , approval of an amendment to certain terms of options ...
Breaking Biology Technology: