The St. Jude researchers determined the shape of a large, paddle-like molecule that Streptococcus pneumoniae bacteria use to latch onto cells lining the throat and lungs. The protein, called CbpA, binds to a molecule on the cell called pIgR, which takes antibodies from the bloodstream on one side of the cell and transports them to the other side. There it releases the antibody at the lining of the throat and lungs. If a pneumococcus bacterium is hovering on the lining of the respiratory tract, this germ binds to pIgR and pushes this antibody shuttle back through the cell to the bloodstream. Once at the other side of the cell, the pneumococcus breaks free of pIgR and enters the blood, where it can multiply and infect the body.
S. pneumoniae is the only bacterium known to use CbpA to invade human cells by binding to pIgR, according to Richard W. Kriwacki, Ph.D., associate member of St. Jude Structural Biology. Kriwacki is senior author of the EMBO Journal report. "The fact that we now know the structure of this important protein means we can begin to develop a vaccine that is more effective in children than those that are currently available," Kriwacki said.
Elaine Tuomanen, M.D., chair of Infectious Diseases and director of the Children's Infection Defense Center at St. Jude, is co-author of the EMBO Journal paper.
"Using CbpA as the key part of a new vaccine against S. pneumoniae would solve a problem that now hinders our ability to protect children from this infection," Tuomanen said.
Current pneumonia vaccines designed to protect adults against more than two dozen strains of S.
Contact: Bonnie Cameron
St. Jude Children's Research Hospital