This latest study on the botulinum neurotoxin was the result of a close collaboration between the Jin group and a research group at the Institute of Toxicology at the Medical School of Hannover, led by Andreas Rummel, Ph.D., an expert on clostridial neurotoxins. They used a technique called X-ray crystallography, which uses powerful X-ray beams to produce 3D images of proteins at the atomic level, to study a genetically inactivated, nontoxic version of the botulinum neurotoxin.
These experiments helped the team visualize the atomic structure of all three parts of the toxin: 1) the region that recognizes neurons, 2) the enzyme that acts like a pair of scissors to cut human neural proteins and cause paralysis, and 3) the needle that punches holes to help deliver the enzyme to the nerve terminal. What's more, the researchers also captured the toxin's interaction with a second bacterial protein, called nontoxic nonhemagglutinin (NTNHA).
"We were surprised to see that NTNHA, which is not toxic, turned out to be remarkably similar to botulinum neurotoxin. It's composed of three parts, just like a copy of the toxin itself. These two proteins hug each other and interlock with what looks like a handshake," said Jin.
As the toxin moves through the body, NTNHA acts as its bodyguard, keeping it from being degraded when times are tough in the acidic stomach. However, as this study revealed, the toxin has a weak spot: when the toxin/NTNHA complex punches its way out of the small intestine, it's the change in pH that triggers a conformational change, breaks up the duo, and releases only the unprotected toxin into the bloodstream.
Towards prevention and therapy
According to Jin, this new knowledge about how the botulinum neurotoxin and NTNHA balance the need for strong binding and a timely release could be exploited to outsmart them.
"We now hope we might be able
|Contact: Heather Buschman, Ph.D.|
Sanford-Burnham Medical Research Institute