The findings were published Jan. 27 in the online version of Nature Immunology.
The protein is called angiogenin 4 (Ang4). It belongs to a class of proteins originally believed to be involved in the formation of blood vessels that supply nutrients to tumors.
This study found that Ang4 is released by Paneth cells, which are located in the intestinal lining. These Paneth cells assist the body's immune system by defending against infection. The researchers tested how Ang4 interacts with a variety of microbes.
They found that Ang4 killed certain kinds of gut microbes. Because of that, the researchers concluded Ang4 may be one of the microbial proteins manufactured by Paneth cells to keep gut bacteria from getting too close to the intestinal lining, where they could cause damage.
The study also found that Ang4 production is controlled by a bacterium that lives in the intestine. The microbe is called Bacteroides thetaiotaomicron. This makes Ang4 the first example of a protein antibiotic whose expression is controlled by friendly intestinal bacteria.
Here's more about gut bacteria and Paneth cells.