PMID: 21055811

Authors:

Clark EA, Crennell S, Upadhyay A, Zozulya AV, Mackay JD, Svergun DI, Bagby S, van den Elsen JM

Title:

A structural basis for Staphylococcal complement subversion: X-ray structure of the complement-binding domain of Staphylococcus aureus protein Sbi in complex with ligand C3d.

Journal:

Mol Immunol. 2010 Nov 3.

Abstract:

The structure of the complement-binding domain of Staphylococcus aureus protein Sbi (Sbi-IV) in complex with ligand C3d is presented. The 1.7A resolution structure reveals the molecular details of the recognition of thioester-containing fragment C3d of the central complement component C3, involving interactions between residues of Sbi-IV helix alpha2 and the acidic concave surface of C3d. The complex provides a structural basis for the binding preference of Sbi for native C3 over C3b and explains how Sbi-IV inhibits the interaction between C3d and complement receptor 2. A second C3d binding site on Sbi-IV is identified in the crystal structure that is not observed in related S. aureus C3 inhibitors Efb-C and Ehp. This binding mode perhaps hints as to how Sbi-IV, as part of Sbi, forms a C3b-Sbi adduct and causes futile consumption of C3, an extraordinary aspect of Sbi function that is not shared by any other known Staphylococcal complement inhibitor.