Berkeley -- University of California, Berkeley, chemists have discovered a trick that anthrax bacteria use to make an end run around the body's defenses, but which may turn out to be their Achilles' heel.
The UC Berkeley scientists, working with colleagues at the University of Mississippi Medical Center in Jackson and the Fred Hutchinson Cancer Research Center in Seattle, uncovered the trick while studying how these deadly bacteria steal iron from their human hosts to grow and reproduce.
"Humans make a protein called siderocalin to defend against bacteria in the continual arms race between pathogen and host. This is the first example of a protein produced by the human immune system that disrupts bacteria's iron scavenging system," said Ken Raymond, UC Berkeley professor of chemistry and faculty scientist at Lawrence Berkeley National Laboratory.
Anthrax bacteria are known to produce two small molecules - bacillibactin and petrobactin - that snatch iron away from the human body's iron transporter molecules, called transferrin. These scavengers, or "siderophores," are essential to anthrax's ability to grow rapidly, especially after the spores are inhaled, though why the bacteria need two siderophores to do the job has been an enigma.
The new study shows why anthrax bacteria require two siderophores working by two different mechanisms. Siderocalin, the human immune protein, binds bacillibactin and effectively sidelines it, the researchers found. Apparently, anthrax fielded a second "stealth" iron scavenger, petrobactin, to get around the human defense against the first scavenger. Petrobactin is not bound by siderocalin.
As far as is known, the human immune system has yet to launch a successful counterattack against the stealth siderophore, but that doesn't mean humans can't design one of their own, according to Raymond. His UC Berkeley team and the Seattle team are now exploring how their discovery could be used to
Contact: Robert Sanders
University of California - Berkeley