Electrostatic contributions drive the interaction between Staphylococcus aureus protein Efb-C and its complement target C3d

Protein Sci. 2008 Nov;17(11):1894-906. doi: 10.1110/ps.036624.108. Epub 2008 Aug 7.


The C3-inhibitory domain of Staphylococcus aureus extracellular fibrinogen-binding protein (Efb-C) defines a novel three-helix bundle motif that regulates complement activation. Previous crystallographic studies of Efb-C bound to its cognate subdomain of human C3 (C3d) identified Arg-131 and Asn-138 of Efb-C as key residues for its activity. In order to characterize more completely the physical and chemical driving forces behind this important interaction, we employed in this study a combination of structural, biophysical, and computational methods to analyze the interaction of C3d with Efb-C and the single-point mutants R131A and N138A. Our results show that while these mutations do not drastically affect the structure of the Efb-C/C3d recognition complex, they have significant adverse effects on both the thermodynamic and kinetic profiles of the resulting complexes. We also characterized other key interactions along the Efb-C/C3d binding interface and found an intricate network of salt bridges and hydrogen bonds that anchor Efb-C to C3d, resulting in its potent complement inhibitory properties.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / genetics
  • Bacterial Proteins / immunology
  • Complement C3d / chemistry*
  • Complement C3d / immunology
  • Computational Biology
  • Crystallization
  • Humans
  • Hydrogen Bonding
  • Point Mutation
  • Protein Binding / physiology
  • Protein Structure, Tertiary / physiology
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / metabolism
  • Staphylococcus aureus / immunology*
  • Static Electricity*
  • Thermodynamics
  • X-Ray Diffraction


  • Bacterial Proteins
  • Efb protein, Staphylococcus aureus
  • Recombinant Proteins
  • Complement C3d