The ultimate decoy: Protein helps bacteria misdirect immune system

A team led by scientists at The Scripps Research Institute (TSRI) has discovered an unusual bacterial protein that attaches to virtually any antibody and prevents it from binding to its target.

Protein M, as it is called, probably helps some bacteria evade the immune response and establish long-term infections.

If follow-up studies confirm Protein M's ability to defeat the antibody response, it is likely to become a target of new antibacterial therapies. The protein's unique ability to bind generally to antibodies also should make it a valuable tool for research and drug development.

"What Protein M does to antibodies represents a very clever trick of evolution," said Richard A. Lerner, MD, Lita Annenberg Hazen Professor of Immunochemistry and Institute Professor at TSRI who led the research.

In a search for factors associated with long-term mycoplasma infection, Rajesh Grover, PhD, a senior staff scientist in the Lerner laboratory, tested samples of antibodies from multiple myeloma patients' blood against a variety of mycoplasma species. One of the proteins recognized by the antibodies was from Mycoplasma genitalium, which causes sexually transmitted infections in humans.

To the scientists' surprise, every antibody sample tested showed reactivity to this protein. But further tests made clear that these antibody reactions were not in response to mass infection with M. genitalium. Instead, the scientists found, the mysterious M. genitalium protein appeared to have evolved simply to bind to any antibody it encounters.