Characterization of the interaction of the pneumococcal surface protein SpsA with the human polymeric immunoglobulin receptor (hpIgR).
OBJECTIVE
The polymeric immunoglobulin receptor (pIgR) is produced by mucosal epithelial cells and plays a crucial role in mucosal immunity. At the basolateral surface of mucosal cells, the pIgR binds predominantly polymeric immunoglobulins, such as dimeric IgA and polymeric IgA (pIgA) and mediates their transport across the polarized cells. This results in apical release of secretory component (SC), either free or bound covalently to IgA, forming secretory IgA (SIgA). The choline-binding protein (Cbp) SpsA, also called PspC and CbpA, has been shown to interact with the pIgR. A hexapeptide motif in SpsA was identified as the minimal binding motif required for binding specifically to pIgR and SC. The present study was carried out to show that the hexapeptide motif in SpsA is crucial for the interaction of pneumococci and pIgR-expressing cells.


METHODS
Streptococcus pneumoniae were cultured to mid-log phase. Calu-3 cells and MDCK epithelial cells, stably transfected with the hpIgR cDNA in pCB6 were used in in vitro infection experiments. Pneumococcal adherence to and invasion of epithelial cells were assayed.


RESULTS
By the use of the N-terminal domain of SpsA and SpsA(201), which exhibits a single amino acid substitution in the pIgR-binding motif, in vitro assays indicated the association of the identified hexapeptide motif, located between amino acid 198 and 203 in SpsA, with pneumococcal adherence to and invasion of hpIgR-expressing cells.


CONCLUSIONS
The present findings demonstrated not only the crucial role of the hexapeptide of SpsA, not only for the SpsA-pIgR interaction, but also for adherence and invasion of hpIgR-expressing cells.
Elm
Christine
C
Department of Microbial Pathogenicity, GBF-National Research Centre for Biotechnology, Braunschweig, Germany.
Rohde
Manfred
M
Vaerman
Jean-Pierre
JP
Chhatwal
Gursharan S
GS
Hammerschmidt
Sven
S
D001422:Bacterial Adhesion; D001426:Bacterial Proteins / Q000378:metabolism*; D002460:Cell Line; D006801:Humans; D011485:Protein Binding; D011971:Receptors, Immunologic / Q000378:metabolism*; D013296:Streptococcus pneumoniae / Q000502:physiology
D001426:Bacterial Proteins; D011971:Receptors, Immunologic; C110344:SpsA protein, Streptococcus pneumoniae