Protein H--a surface protein of Streptococcus pyogenes with separate binding sites for IgG and albumin

Inga-Maria Frick, Per Åkesson, Jakki Cooney, Ulf Sjöbring, Karl-Hermann Schmidt, Hideyuki Gomi, Shizuo Hattori, Chiaki Tagawa, Fumitaka Kishimoto, Lars Björck

Research output: Contribution to journalArticlepeer-review


Protein H, a molecule expressed at the surface of some strains of Streptococcus pyogenes, has affinity for the constant (IgGFc) region of immunoglobulin (Ig) G. In absorption experiments with human plasma, protein H-sepharose could absorb not only IgG but also albumin from plasma. The affinity constant for the reaction between albumin and protein H was 7.8 x 10(9) M-1, which is higher than the affinity between IgG and protein H (Ka = 1.6 x 10(9) M-1). Fragments of protein H were generated with deletion plasmids and polymerase chain reaction (PCR) technology. Using these fragments in various protein-protein interaction assays, the binding of albumin was mapped to three repeats (C1-C3) in the C-terminal half of protein H. On the albumin molecule, the binding site for protein H was found to overlap the site for protein G, another albumin- and IgGFc-binding bacterial surface protein. Also IgGFc-binding could be mapped with the protein H fragments and the region was found N-terminally of the C repeats. A synthetic peptide (25 amino acid residues long) based on a sequence in this region was shown to inhibit the binding of protein H to immobilized IgG or IgGFc. This sequence was not found in previously described IgGFc-binding proteins. However, two other cell surface proteins of S. pyogenes exhibited highly homologous regions. The results identify IgGFc- and albumin-binding regions of protein H and further define and emphasize the convergent evolution among bacterial surface proteins interacting with human plasma proteins.
Original languageEnglish
Pages (from-to)143-151
JournalMolecular Microbiology
Issue number1
Publication statusPublished - 1994

Subject classification (UKÄ)

  • Microbiology in the medical area


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