The SpeB virulence factor of Streptococcus pyogenes, a multifunctional secreted and cell surface molecule with strepadhesin, laminin-binding and cysteine protease activity.

The interactions between pathogenic bacteria and the host need to be resolved at the molecular level in order to develop novel vaccines and drugs. We have previously identified strepadhesin, a novel glycoprotein-binding activity in Streptococcus pyogenes, which is regulated by Mga, a regulator of streptococcal virulence factors. We have now identified the protein responsible for the strepadhesin activity and find that (i) strepadhesin activity is carried by SpeB, streptococcal pyrogenic exotoxin with cysteine protease activity; (ii) SpeB carries laminin-binding activity of the bacteria; and (iii) SpeB is not only a secreted molecule but also occurs unexpectedly tightly bound to the bacterial cell surface. Thus, in contrast to the previous view of SpeB as mainly an extracellular protease, it is also present as a streptococcal surface molecule with binding activity to laminin and other glycoproteins.