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Streptococcal M protein: structural studies of the hypervariable region, free and bound to human C4BP

I André1, J Persson, A M Blom

  • 1Department of Biophysical Chemistry, Lund University, Chemical Center, S-221 00 Lund, Sweden.

Biochemistry
|April 6, 2006
PubMed

Insights

Streptococcus pyogenes M protein's hypervariable region (HVR) adopts a coiled-coil structure, aiding immune evasion. This finding reveals how the M4 HVR binds complement-inhibiting C4BP, crucial for bacterial survival.

Area of Science:

  • Microbiology
  • Structural Biology
  • Immunology

Background:

  • Streptococcus pyogenes utilizes surface M protein as a key virulence factor.
  • The M protein's N-terminal hypervariable region (HVR) is crucial for evading host immunity.
  • Many M protein HVRs bind human C4b-binding protein (C4BP), inhibiting complement activation.

Purpose of the Study:

  • To investigate the structural properties of M protein HVRs from S. pyogenes.
  • To determine if the HVR adopts a coiled-coil structure, similar to other M protein domains.
  • To characterize the interaction between M protein HVRs and C4BP.

Main Methods:

  • Nuclear magnetic resonance (NMR) spectroscopy was used to study M4 and M22 HVRs.
  • Conformational properties were analyzed in isolation and in complex with C4BP.
  • Molecular modeling was employed to propose a structural model.

Main Results:

  • The HVRs of M4 and M22 were determined to be folded as coiled coils.
  • The folded core of the M4 HVR was found to be approximately 27 residues long.
  • The C4BP binding site on M4-N resides within a four-heptad repeat region.

Conclusions:

  • M protein HVRs possess a coiled-coil structure, contributing to their function.
  • The structural insights into M4 HVR-C4BP interaction provide a basis for understanding complement evasion.
  • NMR and modeling data support a structural model for the M4 HVR.

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