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Molecular characteristics of an adhesion molecule containing cholesterol-dependent cytolysin-motif produced by mitis

Airi Matsumoto1, Atsushi Tabata1,2,3, Kazuto Ohkura4

  • 1Department of Biological Science and Technology, Life System, Institute of Technology and Science, Tokushima University Graduate School, Tokushima, Tokushima, Japan.

Microbiology and Immunology
|December 17, 2020
PubMed

Insights

Streptococcus pseudopneumoniae harbors a novel multifunctional protein, mitilectin (MLC), which aids bacterial adhesion to human cells. This protein, also found in related species, is crucial for the pathogenicity of these Streptococcus Mitis group bacteria.

Area of Science:

  • Microbiology
  • Molecular Biology
  • Pathogenesis

Background:

  • Streptococcus pseudopneumoniae (SPpn) is a species closely related to Streptococcus pneumoniae (SPn) and Streptococcus mitis (SM).
  • The pathogenicity of SPpn and the roles of its potential virulence factors remain largely uncharacterized.
  • SPpn possesses genes similar to known pneumococcal virulence factors, necessitating investigation into their function.

Purpose of the Study:

  • To characterize a candidate virulence factor in SPpn with multiple functional domains.
  • To determine the distribution, expression, and function of this gene product across Mitis group of the genus Streptococcus (MGS) species.
  • To assess the role of this factor in the pathogenicity of SPpn and related bacteria.

Main Methods:

  • Bioinformatic analysis and gene sequencing to identify the candidate virulence factor.
  • Expression and purification of recombinant proteins to assess enzymatic and binding activities.
  • Hemolytic assays and human cell-binding assays to evaluate virulence potential.
  • Gene knockout and antibody treatment to confirm the role of the protein in bacterial adhesion.

Main Results:

  • A gene encoding a protein with lipase, lectin, and cytolysin-related domains was identified in SPpn, SM, and SPn.
  • The gene product, named mitilectin (MLC), exhibited lipase and human cell-binding activities but lacked hemolytic activity.
  • MLC was expressed as both secreted and cell-bound forms in positive strains.
  • Anti-MLC antibodies and mlc gene knockout significantly reduced the cell-binding ability of the producing strains.

Conclusions:

  • Mitilectin (MLC) is a multifunctional adhesion molecule found in Mitis group of the genus Streptococcus (MGS) species.
  • MLC plays a significant role in the adherence of SPpn and SM to human cells.
  • MLC is a key factor contributing to the potential pathogenicity of MLC-producing MGS strains.
Keywords:
Mitis group streptococciStreptococcus mitisStreptococcus pseudopneumoniaeadhesion moleculecholesterol-dependent cytolysin

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