Swaminathan and his team had previously analyzed the molecular-level structures of various fragments of botulinum neurotoxin subtypes A to F, and that of the whole neurotoxin B, using x-ray crystallography at the National Synchrotron Light Source (NSLS) at Brookhaven Lab. In this technique, scientists beam high-intensity x-rays at a crystalline sample of the protein and measure how the x-rays scatter off the sample to locate the positions of individual atoms.
These studies revealed that in subtypes A and B, the three domains were arranged in the same way: with the binding and protein-cleaving domains "flanking" a longer central region known as the translocation domain, essential for moving the toxin into the cell.
"Because the genes that code for these proteins have a large degree of similarity and all the subtypes incapacitate nerve cells in a very similar way, many biologists had assumed that all seven botulinum neurotoxins would have a similar structural arrangement," Swaminathan said.
The current study of botulinum subtype E, also conducted at the NSLS, disproved that assumption, taking the scientists by surprise. Instead of the flanking arrangement, the binding and protein-cleaving domains of subtype E are both on the same side of the translocation domain. In addition, while all other subtypes are made of two protein chains, subtype E is a single-chain molecule.
"This arrangement may have an effect on translocation, with the molecule strategically positioned for quick entry into the cell," Swaminathan said. Though he emphasizes that further confirming research is essential, this could be a plausible explanation for why botulism caused by subtype E sets in faster than that caused by other subtypes.
This finding may help scientists develop faster-acting vaccines and therapeutic agents.
For example, in the treatment of hyperactive bladder disorders, botulinum neurotoxin s
|Contact: Karen McNulty Walsh|
DOE/Brookhaven National Laboratory