Cellular location of polyamine transport protein PotD in Streptococcus pneumoniae

Streptococcus pneumoniae encodes a transporter for polyamines that contributes to virulence in an animal model. The putative polyamine-binding protein, PotD, has an amino-terminal secretory peptide but no other domains known to be involved in anchoring proteins to the surface of Gram-positive bacteria. Cell fractionation and immunoblotting, along with flow cytometry, suggest that PotD is surface-exposed and anchored to the cytoplasmic membrane by a potentially novel mechanism.