Researchers have discovered a new bacterial protein with a unique structure that shields antigens from antibodies poised to attack. Dubbed Protein M, the molecule could have implications for developing new antibacterial treatments.
Investigators at the Scripps Research Institute in La Jolla, California, and several other institutions made the discovery while studying multiple myeloma, a B-cell cancer that can result from chronic infection with certain pathogens including Escherichia coli and hepatitis C virus. Their study, published online today in Science, focused on experiments with Mycoplasma, a bacterial parasite that causes chronic infection.
Using samples of antibodies taken from 20 patients with multiple myeloma, the research team found that every antibody sample they tested reacted to a protein produced by Mycoplasma genitalium, which causes human sexually transmitted disease. Protein M, as they named it, didn’t react only with antibodies specifically programmed to fight M genitalium. Protein M could bind to any of the antibodies it encountered, making it a kind of universal decoy that could neutralize the entire antibody response.
The investigators suspect that Protein M evolved to help M genitalium, which has a tiny bacterial genome, survive by fooling the body’s immune response. “The smallest parasitic bacteria on planet Earth seems to have evolved the most sophisticated” evasive mechanism, lead author Rajesh Grover, PhD, of Scripps, said in a statement.
Grover said Protein M’s distinct structure extends “like a tail, over the antibody’s main antigen-binding region.” A search of thousands of known structures in the Protein Data Bank, a worldwide database, came up with none other like it.
“Protein M may be particularly important for large-scale purification of therapeutic antibodies,” Grover and his collaborators wrote. It could also become a target for new drugs aimed at chronic infection with M genitalium and other microbes that can contribute to cancer and inflammatory diseases.