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Related Experiment Videos

Hic, a novel surface protein of Streptococcus pneumoniae that interferes with complement function.

R Janulczyk1, F Iannelli, A G Sjoholm

  • 1Departments of Cell and Molecular Biology, Section for Molecular Pathogenesis, Laboratory Medicine, Section of MIG, Lund University, 22100 Lund, Sweden. Robert.Janulczyk@medkem.lu.se

The Journal of Biological Chemistry
|September 1, 2000
PubMed
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Streptococcus pneumoniae, a pathogen, absorbs factor H using a novel surface protein called Hic. Hic is crucial for factor H binding in type 3 pneumococci, impacting complement inhibition.

Area of Science:

  • Microbiology
  • Immunology
  • Biochemistry

Background:

  • Streptococcus pneumoniae is a significant human pathogen.
  • Complement factor H is a critical inhibitor of the complement system.
  • Pneumococcal surface protein C (PspC) is known to interact with factor H.

Purpose of the Study:

  • To identify and characterize the factor H-binding protein in type 3 Streptococcus pneumoniae.
  • To elucidate the mechanism of factor H acquisition by pneumococci.

Main Methods:

  • Gene identification and sequencing of the pspC locus in type 3 pneumococci.
  • Expression and purification of a recombinant Hic protein fragment (GST:Hic(39-261)).
  • Factor H binding assays using radiolabeled factor H and surface plasmon resonance (SPR).

Related Experiment Videos

  • Analysis of mutant pneumococci lacking the Hic protein.

    • Main Results:

    • A novel surface protein, factor H-binding inhibitor of complement (Hic), was identified in type 3 pneumococci.
    • Hic is anchored to the cell wall and shows low homology to other PspC proteins but shares homology in the N-terminal region.
    • Recombinant Hic fragment bound factor H with high affinity (K(A) = 5 x 10(7)) and inhibited factor H binding to pneumococci.
    • Pneumococcal mutants lacking Hic did not bind factor H, confirming Hic's role in factor H acquisition.
    • Factor H-dependent inhibition of the alternative pathway was not affected, but Hic may possess intrinsic inhibitory properties.

    Conclusions:

    • Hic is the primary factor H-binding protein on type 3 Streptococcus pneumoniae.
    • Hic plays a key role in pneumococcal evasion of the host immune system by acquiring factor H.
    • Further investigation into Hic's potential intrinsic inhibitory activity is warranted.