Submitted April 24, 2008
Accepted October 3, 2008
Staphylococcal SSL5 inhibits leukocyte activation by chemokines and anaphylatoxins
Jovanka Bestebroer*, Kok P.M. van Kessel, Hafida Azouagh, Annemiek M. Walenkamp, Ingrid G.J. Boer, Roland A. Romijn, Jos A.G. van Strijp, and Carla J.C. de Haas
Medical Microbiology, University Medical Center Utrecht, Utrecht, Netherlands
Department of Oncology, University Medical Center Groningen, Groningen, Netherlands
U-Protein Express BV, Utrecht, Netherlands
* Corresponding author; email: j.bestebroer{at}umcutrecht.nl.
Staphylococcus aureus secretes several virulence factors modulating immune responses. Staphylococcal superantigen-like (SSL) proteins are a family of 14 exotoxins with homology to superantigens, but with generally unknown function. Recently, we demonstrated that SSL5 binds to P-selectin glycoprotein ligand 1 dependently of sialyl Lewis X and inhibits P-selectin-dependent neutrophil rolling. Here, we show that SSL5 potently and specifically inhibits leukocyte activation by anaphylatoxins and all classes of chemokines. SSL5 inhibited calcium mobilization, actin polymerization, and chemotaxis induced by chemokines and anaphylatoxins but not by other chemoattractants. Antibody competition experiments showed that SSL5 targets several chemokine and anaphylatoxin receptors. Additionally, transfection studies demonstrated that SSL5 binds glycosylated N-termini of all G protein-coupled receptors (GPCR) but only inhibits stimuli of protein nature that require the receptor N-terminus for activation. Furthermore, SSL5 increased binding of chemokines to cells independent of chemokine receptors through their common glycosaminoglycan-binding site. Importance of glycans was demonstrated for both GPCR and chemokine binding. Thus, SSL5 is an important immunomodulatory protein of S. aureus that targets several crucial, initial stages of leukocyte extravasation. It is therefore a potential new anti-inflammatory compound for diseases associated with chemoattractants and their receptors and disorders characterized by excessive recruitment of leukocytes.
