Protein H--a surface protein of Streptococcus pyogenes with separate binding sites for IgG and albumin.
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.
Frick
I M
IM
Department of Medical and Physiological Chemistry, Lund University, Sweden.
Akesson
P
P
Cooney
J
J
Sjöbring
U
U
Schmidt
K H
KH
Gomi
H
H
Hattori
S
S
Tagawa
C
C
Kishimoto
F
F
Björck
L
L
D000595:Amino Acid Sequence; D001426:Bacterial Proteins; D001483:Base Sequence; D001665:Binding Sites; D001667:Binding, Competitive; D002352:Carrier Proteins / Q000378:metabolism*; D006801:Humans; D007074:Immunoglobulin G / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000378:metabolism; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D012709:Serum Albumin / Q000378:metabolism*; D013297:Streptococcus pyogenes / Q000378:metabolism*
D001426:Bacterial Proteins; D002352:Carrier Proteins; D007074:Immunoglobulin G; D008565:Membrane Proteins; D010446:Peptide Fragments; D011993:Recombinant Fusion Proteins; D012709:Serum Albumin; C064006:protein H, Streptococcus