Cloning and Expression of an Adhesin Antigen of Streptococcus sanguis G9B in Escherichia coli

~~ ~~~~~~~~ A genomic library of Streptococcus sanguis, strain G9B, was constructed and expressed in Escherichia coli using a lgtl 1 expression vector. The amplified library was probed with polyclonal anti-G9B IgG and 13 antigen-positive clones were isolated. A lysate of one clone, designated PP39, absorbed the adhesion-inhibitory activity of anti-G9B IgG. This clone contained an insert of approximately 2000 bp and expressed unique 200 and 53 kDa proteins that reacted with monospecific anti-adhesin antibody. The 200 kDa protein also reacted with anti-pgalactosidase IgG, indicating that it is a fusion protein of which 84 kDa represents the streptococcal adhesin. The 84 and 53 kDa proteins are similar in size to the major polypeptides in a streptococcal antigen complex which is associated with the adhesion of G9B to salivacoated hydroxyapatite. The 53 kDa fragment may result from post-translational cleavage of the recombinant polypeptide.