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The streptococcal cysteine protease SpeB is not a natural immunoglobulin-cleaving enzyme

Helena Persson1, Reine Vindebro, Ulrich von Pawel-Rammingen

  • 1Department of Molecular Biology, Umeå Centre of Microbial Research, Umeå University, Umeå, Sweden.

Infection and Immunity
|April 10, 2013
PubMed

Insights

Streptococcus pyogenes SpeB protease does not degrade immunoglobulins under physiological conditions. Reduced immunoglobulins, lacking function, are cleaved, suggesting SpeB does not aid virulence by degrading Igs.

Area of Science:

  • Microbiology
  • Immunology
  • Biochemistry

Background:

  • Streptococcus pyogenes is a human pathogen employing various virulence factors.
  • The streptococcal cysteine protease SpeB is a key factor in group A streptococcal pathogenesis.
  • SpeB is proposed to degrade human immunoglobulins (Igs), contributing to virulence.

Purpose of the Study:

  • To investigate the immunoglobulin-degrading activity of SpeB under physiological conditions.
  • To determine if SpeB contributes to Streptococcus pyogenes virulence via Ig degradation.

Main Methods:

  • Enzymatic assays to assess SpeB activity on human immunoglobulins.
  • Analysis of Ig cleavage products under varying redox conditions.
  • Evaluation of SpeB's role in virulence considering Ig functional state.

Main Results:

  • SpeB demonstrated no immunoglobulin-cleaving activity under physiological conditions.
  • Only reduced immunoglobulins, existing as semimonomeric molecules, were cleaved by SpeB.
  • Reduced IgG lacks biological effector functions, rendering this cleavage non-pathogenic.

Conclusions:

  • SpeB does not degrade immunoglobulins under physiological conditions relevant to host-pathogen interactions.
  • The proteolytic activity of SpeB on Igs is restricted to non-physiological reduced states.
  • SpeB's contribution to Streptococcus pyogenes virulence is unlikely to be through the degradation of intact immunoglobulins.

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