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Human calprotectin is an iron-sequestering host-defense protein
Toshiki G Nakashige1, Bo Zhang2, Carsten Krebs2,3
1Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
Nature Chemical Biology
|August 25, 2015
Summary
Human calprotectin (CP) sequesters iron, a vital nutrient for bacteria, thereby inhibiting their growth. This discovery reveals a new role for CP in innate immunity and iron regulation.
Area of Science:
- Biochemistry
- Immunology
- Microbiology
Background:
- Human calprotectin (CP) is an innate immune protein known to chelate manganese and zinc.
- The established model suggests CP's antimicrobial function relies on sequestering these metals.
Purpose of the Study:
- To investigate the metal-chelating properties of human calprotectin beyond manganese and zinc.
- To determine if CP chelates iron and if this contributes to its antimicrobial activity.
Main Methods:
- Elemental analysis of growth media treated with CP.
- Microbial growth inhibition studies with bacterial pathogens.
- Biochemical characterization of iron binding to CP, including Mössbauer spectroscopy.
Main Results:
- Elemental analysis confirmed CP reduces manganese, iron, and zinc concentrations in growth media.
- Iron depletion by CP was shown to inhibit bacterial pathogen growth.
- CP coordinates Fe(II) at a hexahistidine motif with subpicomolar affinity in the presence of Ca(II).
Conclusions:
- Human calprotectin actively chelates iron, contributing to its antimicrobial function.
- This finding expands the known roles of CP in innate immunity and mammalian iron homeostasis.
- CP's iron-binding mechanism involves an unusual hexahistidine coordination site activated by calcium.
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