Calprotectin
![Crystal structure of Mn2+ and Ca2+ loaded calprotectin, showing two S100A8-S100A9 dimers. The grey and blue chains represent S100A8 and S100A9, respectively. Purple spheres represent Mn2+ and green spheres represent Ca2+. Only one manganese ion can bind per calprotectin dimer.](/Images/godic/202501/02/Calprotectin-4GGF3112.png")
![His6 coordination of Mn2+ in calprotectin. S100A8 histidine residues are coloured grey, S100A9 histidine residues are coloured purple.](/Images/godic/202501/02/page1-220px-Mn_Centre_Calprotectin-4GGF.pdf3113.jpg")
Calprotectin is a complex of the mammalian proteins S100A8 and S100A9. In the presence of calcium, calprotectin is capable of sequestering the essential nutrients manganese and zinc. This metal sequestration affords the complex antimicrobial properties. Calprotectin is the only known antimicrobial manganese sequestration protein complex. Calprotectin comprises as much as 60% of the soluble protein content of neutrophil cytosol, and is secreted by an unknown mechanism during inflammation. Faecal calprotectin has been used to detect intestinal inflammation, and can serve as a marker for inflammatory bowel diseases. The complex has several synonyms, including MRP8-MRP14, calgranulin A and B, cystic fibrosis antigen, 60BB antigen, and 27E10 antigen.