Characterization of fibrinogen-like protein 2 (FGL2): monomeric FGL2 has enhanced immunosuppressive activity in comparison to oligomeric FGL2

Int J Biochem Cell Biol. 2013 Feb;45(2):408-18. doi: 10.1016/j.biocel.2012.10.014. Epub 2012 Nov 2.


Fibrinogen-like protein 2 (FGL2), a novel effector molecule of CD4(+)CD25(+)Foxp3(+) regulatory T cells (Treg), mediates its suppressive activity through binding to low affinity Fcγ receptors expressed on antigen presenting cells (APCs). FGL2 has been implicated in the pathogenesis of viral hepatitis, xeno- and allotransplant rejection, and rheumatoid arthritis. Here we fully analyzed the structure-function relationships of recombinant murine FGL2 generated in COS-7 cells and identified the receptor binding domains. Native FGL2 exists as an oligomer with a molecular weight of approximately 260 kDa, while under reducing conditions, FGL2 has a molecular weight of 65 kDa suggesting that native FGL2 is composed of four monomers. By site-directed mutation, cysteines at positions 94, 97, 184 and 187, found in the coiled-coil domain were shown to be crucial for FGL2 oligomerization. Monomeric FGL2 had a lower affinity binding to APCs, but increased immunosuppressive activity compared to oligomeric FGL2. Deglycosylation demonstrated that sugar moieties are critical for maintaining solubility of FGL2. SWISS-MODEL analysis suggested that FGL2 has a similar tertiary structure with other members of the fibrinogen family such as fibrinogen and tachylectin. Mutational analysis of cysteine residues and Western blots suggested an asymmetric bouquet-shaped quaternary structure for oligomeric FGL2, resembling many pattern-recognition molecules in the lectin pathway of innate immunity. The functional motifs of FGL2 were mapped to the C terminal globular domain, using a peptide blockade assay. These results collectively define the biochemical and immunological determinants of FGL2, an important immunosuppressive molecule of Treg providing important insights for designing FGL2-related therapeutics.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Amino Acid Substitution
  • Animals
  • COS Cells
  • Cell Proliferation
  • Chlorocebus aethiops
  • Cysteine / chemistry
  • Cysteine / genetics
  • Female
  • Fibrinogen / chemistry
  • Fibrinogen / pharmacology*
  • Fibrinogen / physiology
  • Glycosylation
  • Immunosuppressive Agents / chemistry
  • Immunosuppressive Agents / pharmacology*
  • Mice
  • Mice, Inbred BALB C
  • Models, Molecular
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Peptide Fragments / chemistry
  • Peptide Fragments / pharmacology*
  • Peptide Fragments / physiology
  • Protein Interaction Domains and Motifs
  • Protein Multimerization
  • Protein Processing, Post-Translational
  • Protein Stability
  • Protein Structure, Quaternary
  • Protein Structure, Secondary
  • Solubility
  • T-Lymphocytes / drug effects
  • T-Lymphocytes / immunology
  • T-Lymphocytes / physiology


  • Fgl2 protein, mouse
  • Immunosuppressive Agents
  • Peptide Fragments
  • Fibrinogen
  • Cysteine