In a discovery that can help explain how bacteria infect their hosts, American scientists have claimed that a single atom of calcium controls their movement.
Researchers at the University of North Carolina at Chapel Hill have identified a spot on a human pathogen, Pseudomonas aeruginosa, that when blocked, can stop it in its tracks.
The scientists said, “the finding identifies a key step in the process by which bacteria infect their hosts and could one day lead to new drug targets to prevent infection.”
“When it comes down to it, a single atom makes all the difference,” senior study author Matthew R Redinbo wrote in journal Proceedings of the National Academy of Sciences .
For the last few years, Redinbo and his team has been trying to find out how bacteria’s tiny legs or pili function.
They found that these pili act as grappling hooks — the bacteria extend the fibres out, the fibres attach or stick to a surface and then retracted back into the bacteria, pulling it along.
“This crawling movement is called twitching motility, and without it Pseudomonas, a common cause of hospital — acquired pneumonia, would never be able to move from the lung tissue into the bloodstream, where the infection becomes lethal”.
By resolving the crystal structure of the Pseudomonas’ PilY1 protein, necessary for the creation of pili, they made large amounts of the protein, coaxed it out of solution so that it formed a crystal, and then put the crystal under intense x-ray beams through a process called x-ray diffraction that resulted in a series of spots.
Based on the spots, the researchers calculated what the protein looked like. When they studied the structure, one particular site — the binding site of a calcium atom — looked like it could be important for the function of the protein.
So the researchers began to tinker with the site, looking to see if the changes they made affected the protein’s behaviour.
When they changed the protein so it could no longer bind calcium, the bacteria couldn’t make any legs. When they fooled the protein into thinking it was forever bound to calcium, the bacteria made legs but couldn’t retract them, essentially becoming paralysed.
The results suggested that the protein has to bind calcium to make legs, but it also has to be able to let go of the calcium to pull the legs back in.
“We found it pretty remarkable that the binding of a single atom to a protein that is outside the cell is sufficient to tell these motors that are inside the cell to either stop pushing or stop pulling,” said Redinbo.
