High-Affinity Interactions of Beryllium(2+) with Phosphatidylserine Result in a Cross-Linking Effect Reducing Surface Recognition of the Lipid

Biochemistry. 2017 Oct 10;56(40):5457-5470. doi: 10.1021/acs.biochem.7b00644. Epub 2017 Sep 20.

Abstract

Beryllium has multiple industrial applications, but its manufacture is associated with a serious occupational risk of developing chronic inflammation in the lungs known as berylliosis, or chronic beryllium disease. Although the Be2+-induced abnormal immune responses have recently been linked to a specific MHC-II allele, the nature of long-lasting granulomas is not fully understood. Here we show that Be2+ binds with a micromolar affinity to phosphatidylserine (PS), the major surface marker of apoptotic cells. Isothermal titration calorimetry indicates that, like that of Ca2+, binding of Be2+ to PS liposomes is largely entropically driven, likely by massive desolvation. Be2+ exerts a compacting effect on PS monolayers, suggesting cross-linking through coordination by both phosphates and carboxyls in multiple configurations, which were visualized in molecular dynamics simulations. Electrostatic modification of PS membranes by Be2+ includes complete neutralization of surface charges at ∼30 μM, accompanied by an increase in the boundary dipole potential. The data suggest that Be2+ can displace Ca2+ from the surface of PS, and being coordinated in a tight shell of four oxygens, it can mask headgroups from Ca2+-mediated recognition by PS receptors. Indeed, 48 μM Be2+ added to IC-21 cultured macrophages specifically suppresses binding and engulfment of PS-coated silica beads or aged erythrocytes. We propose that Be2+ adsorption at the surface of apoptotic cells may potentially prevent normal phagocytosis, thus causing accumulation of secondary necrotic foci and the resulting chronic inflammation.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Beryllium / metabolism*
  • Macrophages / metabolism
  • Molecular Conformation
  • Molecular Dynamics Simulation
  • Phosphatidylserines / chemistry
  • Phosphatidylserines / metabolism*
  • Static Electricity
  • Surface Properties

Substances

  • Phosphatidylserines
  • Beryllium