The extracellular adherence protein from Staphylococcus aureus inhibits the classical and lectin pathways of complement by blocking formation of the C3 proconvertase.
The pathogenic bacterium Staphylococcus aureus actively evades many aspects of human innate immunity by expressing a series of small inhibitory proteins. A number of these proteins inhibit the complement system, which labels bacteria for phagocytosis and generates inflammatory chemoattractants. Although the majority of staphylococcal complement inhibitors act on the alternative pathway to block the amplification loop, only a few proteins act on the initial recognition cascades that constitute the classical pathway (CP) and lectin pathway (LP). We screened a collection of recombinant, secreted staphylococcal proteins to determine whether S. aureus produces other molecules that inhibit the CP and/or LP. Using this approach, we identified the extracellular adherence protein (Eap) as a potent, specific inhibitor of both the CP and LP. We found that Eap blocked CP/LP-dependent activation of C3, but not C4, and that Eap likewise inhibited deposition of C3b on the surface of S. aureus cells. In turn, this significantly diminished the extent of S. aureus opsonophagocytosis and killing by neutrophils. This combination of functional properties suggested that Eap acts specifically at the level of the CP/LP C3 convertase (C4b2a). Indeed, we demonstrated a direct, nanomolar-affinity interaction of Eap with C4b. Eap binding to C4b inhibited binding of both full-length C2 and its C2b fragment, which indicated that Eap disrupts formation of the CP/LP C3 proconvertase (C4b2). As a whole, our results demonstrate that S. aureus inhibits two initiation routes of complement by expression of the Eap protein, and thereby define a novel mechanism of immune evasion.
Department of Biochemistry & Molecular Biophysics; Kansas State University, Manhattan, KS, USA.
Jordan L
JL
Woehl
Medical Microbiology; University Medical Center Utrecht, Utrecht, The Netherlands.
Daphne A C
DAC
Stapels
School of Biological Sciences; University of Missouri-Kansas City, Kansas City, MO, USA.
Brandon L
BL
Garcia
Department of Biochemistry & Molecular Biophysics; Kansas State University, Manhattan, KS, USA.
Kasra X
KX
Ramyar
School of Biological Sciences; University of Missouri-Kansas City, Kansas City, MO, USA.
Andrew
A
Keightley
Medical Microbiology; University Medical Center Utrecht, Utrecht, The Netherlands.
Maartje
M
Ruyken
Department of Pathology & Laboratory Medicine; University of Pennsylvania, Philadelphia, PA, USA.
Maria
M
Syriga
Department of Pathology & Laboratory Medicine; University of Pennsylvania, Philadelphia, PA, USA.
Georgia
G
Sfyroera
School of Biological Sciences; University of Missouri-Kansas City, Kansas City, MO, USA.
Alexander B
AB
Weber
Department of Biochemistry & Molecular Biophysics; Kansas State University, Manhattan, KS, USA.
Michal
M
Zolkiewski
Department of Pathology & Laboratory Medicine; University of Pennsylvania, Philadelphia, PA, USA.
Daniel
D
Ricklin
Department of Pathology & Laboratory Medicine; University of Pennsylvania, Philadelphia, PA, USA.
John D
JD
Lambris
Medical Microbiology; University Medical Center Utrecht, Utrecht, The Netherlands.
Suzan H M
SHM
Rooijakkers
School of Biological Sciences; University of Missouri-Kansas City, Kansas City, MO, USA.|Department of Biochemistry & Molecular Biophysics; Kansas State University, Manhattan, KS, USA.
Brian V
BV
Geisbrecht
D001426:Bacterial Proteins / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism*; D001665:Binding Sites; D003175:Complement C2 / Q000276:immunology / Q000378:metabolism; D051561:Complement C3 Convertase, Alternative Pathway / Q000037:antagonists & inhibitors*; D003179:Complement C3b / Q000276:immunology / Q000378:metabolism; D015935:Complement C4b / Q000276:immunology / Q000378:metabolism; D003171:Complement Pathway, Classical / Q000276:immunology*; D037582:Complement Pathway, Mannose-Binding Lectin / Q000276:immunology*; D003602:Cytotoxicity, Immunologic; D006801:Humans; D018448:Models, Immunological; D009504:Neutrophils / Q000276:immunology; D010587:Phagocytosis / Q000276:immunology; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism*; D013203:Staphylococcal Infections / Q000276:immunology / Q000378:metabolism; D013211:Staphylococcus aureus / Q000276:immunology* / Q000378:metabolism*
D001426:Bacterial Proteins; D003175:Complement C2; C444739:Eap-N protein, Staphylococcus aureus; D016601:RNA-Binding Proteins; D003179:Complement C3b; D015935:Complement C4b; D051561:Complement C3 Convertase, Alternative Pathway