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Trimeric structure and conformational equilibrium of M-ficolin fibrinogen-like domain

Michikazu Tanio1, Shin Kondo, Shigetoshi Sugio

  • 1Mitsubishi Kagaku Institute of Life Sciences (MITILS), 11 Minamiooya, Machida, Tokyo 194-8511, Japan.

Journal of Synchrotron Radiation
|April 19, 2008
PubMed

Insights

Human M-ficolin recognition domain (FD1) structure reveals a unique peptide bond. This structural difference, involving cis-trans isomerization, is key to how ficolins distinguish between self and non-self molecules in innate immunity.

Area of Science:

  • Structural biology
  • Immunology
  • Biochemistry

Background:

  • Ficolins are crucial pathogen-recognition molecules in innate immune systems.
  • Understanding their structure is vital for elucidating immune response mechanisms.

Purpose of the Study:

  • To determine the crystal structure of the human M-ficolin recognition domain (FD1).
  • To compare FD1 structure with related proteins and investigate its ligand-binding properties.

Main Methods:

  • X-ray crystallography at 1.9 Å resolution.
  • Comparative structural analysis.
  • Analysis of pH-dependent ligand-binding activity in solution.

Main Results:

  • The crystal structure of FD1 was determined, showing similarity to other fibrinogen-related proteins.
  • A distinct trans peptide bond between Asp282 and Cys283 was observed in FD1's ligand-binding site.
  • pH-dependent binding studies indicated a conformational equilibrium involving cis-trans isomerization of this peptide bond.

Conclusions:

  • The unique Asp282-Cys283 peptide bond and its isomerization are critical for M-ficolin's self/non-self discrimination.
  • This mechanism contributes to the innate immune system's ability to target pathogens effectively.

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