Structure-function analysis of the C3 binding region of Staphylococcus aureus immune subversion protein Sbi

Abhisek Upadhyay, Julia D. Burman, Elizabeth A. Clark, Elisa Leung, David E. Isenman, Jean M. H. van den Elsen, Stefan Bagby

Research output: Contribution to journalArticle

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Abstract

Among the recently discovered Staphylococcus aureus immune evasion proteins, Sbi is unique in its ability to interact with components of both the adaptive and innate immune systems of the host. Sbi domains I and II (Sbi-I and Sbi-II) bind IgG. Sbi domain IV (residues 198–266) binds the central complement protein C3. When linked to Sbi-III, Sbi-IV induces a futile consumption of complement via alternative pathway activation, whereas isolated Sbi-IV specifically inhibits the alternative pathway without complement consumption. Here we have determined the three-dimensional structure of Sbi-IV by NMR spectroscopy, showing that Sbi-IV adopts a three-helix bundle fold similar to those of the S. aureus complement inhibitors Efb-C, Ehp, and SCIN. The 1H-15N HSQC spectrum of Sbi-III indicates that this domain, essential for futile complement consumption, is natively unfolded, at least when isolated from the rest of Sbi. Sbi-IV and Sbi-III-IV both bind C3dg with 1:1 stoichiometry and submicromolar affinity. Despite low overall sequence identity, Sbi possesses the same residues as Efb at two positions essential for Efb-C binding to C3d. Mutation to alanine of either of these residues, Arg-231 and Asn-238, abolishes both Sbi-IV binding to C3dg and Sbi-IV alternative pathway inhibition. The almost complete conservation of Sbi-III and Sbi-IV amino acid sequences across more than 30 strains isolated from human and animal hosts indicates that the unique mechanism of Sbi in complement system subversion is a feature of infections of both humans and economically important animals.
Original languageEnglish
Pages (from-to)22113-22120
Number of pages8
JournalJournal of Biological Chemistry
Volume283
Issue number32
Early online date10 Jun 2008
DOIs
Publication statusPublished - 8 Aug 2008

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Alternative Complement Pathway
Complement Inactivating Agents
Staphylococcus aureus
Animals
Immune Evasion
Complement C3
Immune system
Stoichiometry
Alanine
Nuclear magnetic resonance spectroscopy
Amino Acid Sequence
Immune System
Conservation
Complement System Proteins
Proteins
Magnetic Resonance Spectroscopy
Immunoglobulin G
Chemical activation
Amino Acids
Mutation

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Structure-function analysis of the C3 binding region of Staphylococcus aureus immune subversion protein Sbi. / Upadhyay, Abhisek; Burman, Julia D.; Clark, Elizabeth A.; Leung, Elisa; Isenman, David E.; van den Elsen, Jean M. H.; Bagby, Stefan.

In: Journal of Biological Chemistry, Vol. 283, No. 32, 08.08.2008, p. 22113-22120.

Research output: Contribution to journalArticle

Upadhyay, Abhisek ; Burman, Julia D. ; Clark, Elizabeth A. ; Leung, Elisa ; Isenman, David E. ; van den Elsen, Jean M. H. ; Bagby, Stefan. / Structure-function analysis of the C3 binding region of Staphylococcus aureus immune subversion protein Sbi. In: Journal of Biological Chemistry. 2008 ; Vol. 283, No. 32. pp. 22113-22120.
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