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Isolation of Labile Multi-protein Complexes by in vivo Controlled Cellular Cross-Linking and Immuno-magnetic Affinity Chromatography
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Isolation of Labile Multi-protein Complexes by in vivo Controlled Cellular Cross-Linking and Immuno-magnetic Affinity Chromatography

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Complex between Peptostreptococcus magnus protein L and a human antibody reveals structural convergence in the

M Graille1, E A Stura, N G Housden

  • 1Département d'Ingénierie et d'Etudes des Protéines, Commissariat à l'Energie Atomique, Centre d'Etudes Saclay, F-91191, Gif-sur-Yvette, France.

Structure (London, England : 1993)
|October 6, 2001
PubMed
Abstract

Insights

Peptostreptococcus magnus protein L (PpL) binds to human antibody light chains outside the typical antigen-binding site. This bacterial virulence factor interacts with kappa light chains via two distinct interfaces, explaining its specificity.

Area of Science:

  • Structural biology
  • Immunology
  • Microbial pathogenesis

Background:

  • Peptostreptococcus magnus protein L (PpL) is a bacterial surface protein associated with virulence.
  • PpL possesses immunoglobulin-binding domains that interact with the variable light (VL) regions of kappa light chains in mammalian antibodies.

Purpose of the Study:

  • To elucidate the structural basis of the interaction between a single PpL domain and a human antibody Fab fragment.
  • To understand the molecular mechanisms underlying PpL's specificity for kappa light chains.

Main Methods:

  • Refined crystal structure analysis of the PpL-Fab complex at 2.7 Å resolution.
  • Site-directed mutagenesis and analytical ultracentrifugation to assess binding affinities.

Main Results:

  • The crystal structure revealed two independent binding interfaces between a single PpL domain and two antibody Fab molecules, targeting VL framework regions.
  • One interface confirmed previous biochemical data, while the second was novel.
  • PpL binding sites exhibited differential affinities for VL, and PpL residues involved are conserved across bacterial strains.
  • The identified contact points explain PpL's specificity for kappa over lambda light chains.

Conclusions:

  • This study presents the first structure of a bacterial virulence factor binding to an antibody light chain outside the conventional antigen-binding site.
  • PpL shares a similar binding mode and beta-zipper interaction with streptococcal protein G (SpG) domains, another bacterial protein that binds immunoglobulin.
  • The findings offer insights into bacterial immune evasion strategies and potential therapeutic targets.

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