Staphylococcal superantigen-like protein 10 (SSL10) binds to human immunoglobulin G (IgG) and inhibits complement activation via the classical pathway.
Staphylococcal superantigen-like (SSL) proteins are a family of exoproteins that share structural similarity with staphylococcal superantigens but exhibit no superantigenic activity. It was previously reported that two members (SSL5 and SSL7) bound to serum components and cell adhesion molecules involved in host immune response; however, the other family members have not been functionally characterized. In this study, we attempted to isolate SSL10-binding proteins from human serum and found that recombinant His-tagged SSL10 bound two major polypeptides of approximately 50 and approximately 25 kDa after affinity purification and SDS-polyacrylamide gel electrophoresis. These polypeptides were identified as heavy and light chains of human IgG by peptide mass fingerprinting analysis. The specific interaction between recombinant SSL10 and human IgG was confirmed by far Western blot analysis using immobilized SSL10 and pull-down analysis using SSL10-conjugated Sepharose. Surface plasmon resonance analysis revealed that the dissociation equilibrium constant for the interaction between human IgG and recombinant SSL10 was estimated to be 220 nM. We also found that recombinant SSL10 inhibited the binding of complement component C1q to IgG-Sepharose and hemolysis of IgG-sensitized sheep erythrocytes via the classical complement activation pathway. These results suggest that SSL10 may play a role in the evasion of Staphylococcus aureus from the host immune system via interfering complement activation.
Itoh
Saotomo
S
Department of Microbiology, Hoshi University, School of Pharmacy and Pharmaceutical Sciences, Tokyo 142-8501, Japan.
Hamada
Eri
E
Kamoshida
Go
G
Yokoyama
Ryosuke
R
Takii
Takemasa
T
Onozaki
Kikuo
K
Tsuji
Tsutomu
T
D000595:Amino Acid Sequence; D000818:Animals; D000942:Antigens, Bacterial / Q000276:immunology*; D001426:Bacterial Proteins / Q000276:immunology*; D015922:Complement C1q / Q000276:immunology; D003171:Complement Pathway, Classical / Q000276:immunology*; D004591:Electrophoresis, Polyacrylamide Gel; D006461:Hemolysis / Q000276:immunology; D006639:Histidine; D006801:Humans; D055767:Immobilized Proteins; D007074:Immunoglobulin G / Q000737:chemistry / Q000276:immunology*; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D009842:Oligopeptides; D011485:Protein Binding / Q000276:immunology; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012756:Sheep; D013211:Staphylococcus aureus / Q000276:immunology*; D018089:Superantigens / Q000276:immunology*; D020349:Surface Plasmon Resonance
D000942:Antigens, Bacterial; D001426:Bacterial Proteins; C471213:His-His-His-His-His-His; D055767:Immobilized Proteins; D007074:Immunoglobulin G; D009842:Oligopeptides; D011993:Recombinant Fusion Proteins; C000619943:SSL10 protein, Staphylococcus aureus; D018089:Superantigens; D006639:Histidine; D015922:Complement C1q