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Histidine-mediated pH-sensitive regulation of M-ficolin:GlcNAc binding activity in innate immunity examined by

Lifeng Yang1, Jing Zhang, Bow Ho

  • 1Computational and Systems Biology, Singapore-MIT Alliance, Singapore, Singapore.

Plos One
|May 17, 2011
PubMed
Abstract

Insights

M-ficolin

Area of Science:

  • Immunology
  • Biochemistry
  • Structural Biology

Background:

  • M-ficolin is a key innate immune molecule recognizing N-acetyl-D-glucosamine (GlcNAc) on microbes and apoptotic cells.
  • A cis-trans isomerization of the Asp282-Cys283 peptide bond in M-ficolin influences GlcNAc binding.
  • Understanding pH-dependent conformational changes is vital for immune surveillance and apoptotic cell clearance.

Purpose of the Study:

  • To elucidate the pH-mediated mechanism of GlcNAc binding by M-ficolin.
  • To investigate the role of the Asp282-Cys283 peptide bond isomerization in M-ficolin's activity.
  • To determine the influence of pH on M-ficolin's conformational equilibrium.

Main Methods:

  • Immunodetection analysis to assess GlcNAc binding.
  • Constant pH molecular dynamics (MD) simulations at various pH values.
  • Hydrogen bond occupancy analysis of wild-type M-ficolin and histidine mutants (H251A, H284A, H297A).

Main Results:

  • M-ficolin's GlcNAc binding is regulated by a pH-sensitive conformational equilibrium.
  • His284 is essential for pH-dependent GlcNAc binding, mediating the Asp282-Cys283 isomerization.
  • His297 influences pH-dependent isomerization, particularly in weakly basic conditions.

Conclusions:

  • The cis isomer of the Asp282-Cys283 peptide bond, prevalent at neutral pH, facilitates GlcNAc binding.
  • Acidic pH promotes the trans isomer, reducing GlcNAc binding affinity.
  • MD simulations reveal His284 protonation drives the isomerization crucial for M-ficolin's ligand-binding activity.

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