Identification of human plasma C1 inhibitor as a target protein for staphylococcal superantigen-like protein 5 (SSL5)

The family of staphylococcal superantigen-like proteins (SSLs) have a structure similar to bacterial superantigens but exhibit no superantigenic activity. These exoproteins have recently been shown to disturb the host immune defense system. One family member, SSL5, was reported to bind to human leuk...

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Bibliographic Details
Published in:Biochemical and biophysical research communications 2019-01, Vol.508 (4), p.1162-1167
Main Authors: Oku, Teruaki, Kurisaka, Chisato, Ando, Yusuke, Tsuji, Tsutomu
Format: Article
Language:English
Subjects:
C1 inhibitor
Complement
Immune perturbation
Sialic acid
SSL5
Staphylococcus aureus
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Summary:The family of staphylococcal superantigen-like proteins (SSLs) have a structure similar to bacterial superantigens but exhibit no superantigenic activity. These exoproteins have recently been shown to disturb the host immune defense system. One family member, SSL5, was reported to bind to human leukocyte P-selectin glycoprotein ligand-1 (PSGL-1) and matrix metalloproteinase-9 (MMP-9) and to interfere with leukocyte trafficking. In the present study, we explored human plasma proteins bound by glutathione S-transferase (GST)-tagged recombinant SSL5 (GST-SSL5) and identified plasma protease C1 inhibitor (C1Inh) as a major SSL5-binding protein based on the results of peptide mass fingerprinting analysis with MALDI-TOFMS. GST-SSL5 was found to attenuate the inhibitory activity of recombinant histidine-tagged C1Inh (C1Inh-His) toward complement C1s. We also observed that the treatment of C1Inh-His with neuraminidase markedly decreased its binding to GST-SSL5. Moreover, C1Inh-His produced by Lec2 mutant cells (deficient in sialic acid biosynthesis) showed much lower binding affinity for SSL5 than that produced by the wild-type CHO-K1 cells, as assessed by pull-down assay. These results suggest that SSL5 binds to C1Inh in a sialic acid-dependent fashion and modulates the host immune defense through perturbation of the complement system in association with S. aureus infection. •Staphylococcal superantigen-like protein 5 (SSL5) binds to human plasma C1 inhibitor.•SSL5 reduces the inhibitory effect of C1 inhibitor against complement C1s activity.•Sialic acid-containing glycans of C1 inhibitor are involved in its binding to SSL5.
ISSN:0006-291X
1090-2104
DOI:10.1016/j.bbrc.2018.12.026