Streptococcus pneumoniae is a Gram-positive bacterium that has evolved several sophisticated mechanisms to evade the human innate immune system. One strategy is to bind human complement regulators to inhibit the complement system directly on the surface of the pathogen. The surface exposed protein Hic binds the human complement inhibitor Factor H and thereby uses its function to block the complement attack. Here, we use Hic heterologously expressed on the surface of Lactococcus lactis (intact bacteria) to analyze the binding of the human complement regulator Factor H. The plasmid-encoded Hic protein is anchored to the peptidoglycan via Sortase A on the surface of the bacterial strain and this system is used as a tool to analyze the function of the protein of interest on an avirulent bacterial strain lacking all other S. pneumoniae proteins. L. lactis containing an empty vector (not expressing Hic on the surface) is used as a negative control.

protein – protein interaction | whole bacteria | MO-P-063