Details of Bacterial ‘Injection’ System Revealed

Apr 26, 2009
Details of bacterial 'injection' system revealed
STEM image showing isolated needle complexes marked with rectangles for mass analysis. Rods are TMV (tobacco mosaic virus) particles used for reference.

(PhysOrg.com) -- New details of the composition and structure of a needlelike protein complex on the surface of certain bacteria may help scientists develop new strategies to thwart infection. The research, conducted in part at the U.S. Department of Energy's Brookhaven National Laboratory, will be published April 26, 2009, in the advance online edition of Nature Structural & Molecular Biology.

The scientists were studying a needlelike complex known as a "type III secretion system," or T3SS, on the surface of Shigella , a cause of dysentery. The secretion system is a complex protein structure that traverses the bacterial cell membrane and acts as a biological syringe to inject deadly proteins into intestinal cells. These proteins rupture the cell's innards, leading to bloody diarrhea and sometimes death. Similar secretion systems exist in a range of other infectious bacteria, including those that cause typhoid fever, some types of food poisoning, and plague.

"Understanding the 3D structure of these secretion proteins is important for the design of new broad-spectrum strategies to combat bacterial infections," said study co-author Joseph Wall, a biophysicist at Brookhaven Lab.

Previous studies of the type III secretion system have revealed that it is composed of some 25 different kinds of proteins assembled into three major parts: a "bulb" that lies within the bacterial cell, a region spanning the inner and outer bacterial membranes, and a hollow, largely extracellular "needle." But to understand how the parts work together to secrete proteins, the scientists required higher-resolution structural information, and knowledge of the chemical makeup and arrangement of the components.

Using a combination of scanning transmission electron microscopy (STEM) and transmission electron microscopy (TEM), the scientists have now revealed new details of the "needle complex" structure.

"STEM and the other techniques work in complementary ways," said Wall, who designed and runs the STEM facility at Brookhaven Lab. By itself, STEM cannot reveal a structure, but it gives very accurate sizes of the molecules making up particular parts, which helps scientists hone in on the structure hinted at by the other techniques. STEM also allows only good, intact molecules to be selected for analysis, which avoids errors inherent in bulk measures of mixtures of intact and broken complexes, a problem that may have affected previous analyses.

"Our reconstruction shows an overall size, shape and major sub-component arrangement consistent with previous studies," said Wall. "However, the new structure also reveals details of individual subunits and their angular orientation, which changes direction over the structure's length. We now see 12-fold symmetric features and details of connections between sub-domains both internally and externally throughout the 'needle' base."

The more accurate model therefore shows how the different parts of the injection machine fit together and may fit with other bacterial components that provide the engine to drive injection. These are important steps toward developing a detailed understanding of how the injection machine works, and to developing inhibitors that can prevent bacterial infections.

Although STEM was built more than 25 years ago, it remains a state-of-the-art tool for accurately determining the stoichiometry and homogeneity of biological complexes. It is one of the unique tools that Brookhaven Lab provides to the scientific community.

In the case of this study, said lead author Ariel Blocker of Oxford University and the University of Bristol, UK, "The STEM experiment was key because it provided unique and independent information that allowed the narrowing down of potential symmetries within the structure to a small set of testable possibilities."

Source: Brookhaven National Laboratory (news : web)

Explore further: Genomes of malaria-carrying mosquitoes sequenced

add to favorites email to friend print save as pdf

Related Stories

Structures of important plant viruses determined

Oct 01, 2008

Flexible filamentous viruses make up a large fraction of known plant viruses and are responsible for more than half the viral damage to crop plants throughout the world. New details of their structures, which were poorly ...

Structure reveals how cells 'sugar-coat' proteins

Mar 11, 2008

Biologists at the U.S. Department of Energy's Brookhaven National Laboratory, Stony Brook University, and the University of Wurzburg, Germany, have deciphered the structure of a large protein complex responsible for adding ...

Scientists look at 'syringe' assembly in plague bacteria

Feb 27, 2008

Bacteria that cause the bubonic plague avoid death in our bodies by injecting our cells with immune evasion proteins. Scientists have discovered a new way bacteria build and hold the syringes, according to research published ...

Structure mediating spread of antibiotic resistance identified

Jan 08, 2009

Scientists have identified the structure of a key component of the bacteria behind such diseases as whooping cough, peptic stomach ulcers and Legionnaires' disease. The research, funded by the Wellcome Trust and the Biotechnology ...

Following Nature's Lead, Scientists Seek Better Catalysts

Jan 24, 2005

Iron-sulfur nanosystem isolated from bacterium is more reactive than catalysts in use Those seeking to design more efficient catalysts for the production of hydrogen and the control of air pollutants might do well to take ...

Recommended for you

Genomes of malaria-carrying mosquitoes sequenced

Nov 27, 2014

Nora Besansky, O'Hara Professor of Biological Sciences at the University of Notre Dame and a member of the University's Eck Institute for Global Health, has led an international team of scientists in sequencing ...

How calcium regulates mitochondrial carrier proteins

Nov 26, 2014

Mitochondrial carriers are a family of proteins that play the key role of transporting a chemically diverse range of molecules across the inner mitochondrial membrane. Mitochondrial aspartate/glutamate carriers are part of ...

Team conducts unprecedented analysis of microbial ecosystem

Nov 26, 2014

An international team of scientists from the Translational Genomics Research Institute (TGen) and The Luxembourg Centre for Systems Biomedicine (LCSB) have completed a first-of-its-kind microbial analysis of a biological ...

Students create microbe to weaken superbug

Nov 25, 2014

A team of undergraduate students from the University of Waterloo have designed a synthetic organism that may one day help doctors treat MRSA, an antibiotic-resistant superbug.

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.