Human and pneumococcal cell surface glyceraldehyde-3-phosphate dehydrogenase (GAPDH) proteins are both ligands of human C1q protein

J Biol Chem. 2012 Dec 14;287(51):42620-33. doi: 10.1074/jbc.M112.423731. Epub 2012 Oct 18.

Abstract

C1q, a key component of the classical complement pathway, is a major player in the response to microbial infection and has been shown to detect noxious altered-self substances such as apoptotic cells. In this work, using complementary experimental approaches, we identified the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) as a C1q partner when exposed at the surface of human pathogenic bacteria Streptococcus pneumoniae and human apoptotic cells. The membrane-associated GAPDH on HeLa cells bound the globular regions of C1q as demonstrated by pulldown and cell surface co-localization experiments. Pneumococcal strains deficient in surface-exposed GAPDH harbored a decreased level of C1q recognition when compared with the wild-type strains. Both recombinant human and pneumococcal GAPDHs interacted avidly with C1q as measured by surface plasmon resonance experiments (K(D) = 0.34-2.17 nm). In addition, GAPDH-C1q complexes were observed by transmission electron microscopy after cross-linking. The purified pneumococcal GAPDH protein activated C1 in an in vitro assay unlike the human form. Deposition of C1q, C3b, and C4b from human serum at the surface of pneumococcal cells was dependent on the presence of surface-exposed GAPDH. This ability of C1q to sense both human and bacterial GAPDHs sheds new insights on the role of this important defense collagen molecule in modulating the immune response.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoptosis
  • Cell Membrane / enzymology*
  • Cell Membrane Structures / metabolism
  • Complement Activation
  • Complement C1q / chemistry
  • Complement C1q / metabolism*
  • Complement C1q / ultrastructure
  • Glyceraldehyde-3-Phosphate Dehydrogenases / metabolism*
  • Glyceraldehyde-3-Phosphate Dehydrogenases / ultrastructure
  • HeLa Cells
  • Humans
  • Immobilized Proteins / metabolism
  • Kinetics
  • Ligands
  • Mutation / genetics
  • Plasminogen / metabolism
  • Protein Binding
  • Protein Transport
  • Solubility
  • Solutions
  • Streptococcus pneumoniae / enzymology*
  • Surface Plasmon Resonance

Substances

  • Immobilized Proteins
  • Ligands
  • Solutions
  • Complement C1q
  • Plasminogen
  • Glyceraldehyde-3-Phosphate Dehydrogenases