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Portrait of Tommy Cedervall; Photo: Kennet Ruona

Tommy Cedervall

Associate Professor, Coordinator Nanosafety

Portrait of Tommy Cedervall; Photo: Kennet Ruona

Coiled-coil structure of group A streptococcal M proteins. Different temperature stability of class A and C proteins by hydrophobic-nonhydrophobic amino acid substitutions at heptad positions a and d


  • T Cedervall
  • M U Johansson
  • B Akerström

Summary, in English

M proteins and M-like proteins, expressed on the surface of group A streptococci and binding to human plasma proteins, can be divided into two classes, A and C, depending on the structure of the central repeated regions. The class C proteins have been shown to be dimers with a coiled-coil structure. In this work, we have compared the structure and binding of a class A protein, Mrp4, and a class C protein, Arp4, expressed by the same bacterial strain. Circular dichroism spectra, gel filtration, and binding assays showed that both proteins had a coiled-coil dimer configuration and a high-affinity binding at 20 degrees C. However, striking differences were seen at 37 degrees C. The class A protein, Mrp4, was still a coiled-coil dimer with high affinity binding activity, whereas the class C protein, Arp4, had lost both the coiled-coil structure and binding activity. Raising the temperature even higher, Mrp4 retained the coiled-coil structure up to 70-90 degrees C. Furthermore, a recombinant protein, Mrp(C), in which the A-repeats of Mrp4 were replaced by the C-repeats of Arp4, lost its coiled-coil structure and fibrinogen-binding around 40-45 degrees C. These results suggest a high thermal stability of class A proteins and a low stability of class C proteins and that the structural basis for this can be found partly in the A- and C-repeats. Analysis of the amino acid sequences of the A- and C-repeats, revealed a large difference, 87% and 45%, respectively, in the content of hydrophobic amino acid residues in the positions regarded as important for the formation of the coiled-coil structure. In particular, several alanine residues in the A-repeats were replaced by serine residues in the C-repeats. Our results suggest that important structural and functional changes within the M protein family have evolved by specific hydrophobic-nonhydrophobic amino acid replacements.


  • Biochemistry and Structural Biology
  • Biophysical Chemistry

Publishing year












Document type

Journal article


The American Chemical Society (ACS)


  • Cell and Molecular Biology


  • Amino Acid Sequence
  • Amino Acids/analysis
  • Antigens, Bacterial/chemistry
  • Antigens, Surface/chemistry
  • Bacterial Outer Membrane Proteins
  • Bacterial Proteins/chemistry
  • Carrier Proteins/chemistry
  • Chromatography, Gel
  • Circular Dichroism
  • Fibrinogen/metabolism
  • Hot Temperature
  • Humans
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Protein Conformation
  • Protein Structure, Secondary
  • Recombinant Proteins/metabolism
  • Streptococcus pyogenes/chemistry
  • Structure-Activity Relationship




  • ISSN: 0006-2960