calprotectin complex

Calprotectin is a complex of the mammalian proteins S100A8 and S100A9. Other names for calprotectin include MRP8-MRP14, calgranulin A and B, cystic fibrosis antigen, L1, 60BB antigen, and 27E10 antigen. The proteins exist as homodimers but preferentially exist as S100A8/A9 heterodimers or heterotetramers (calprotectin) with antimicrobial, proinflammatory and prothrombotic properties. In the presence of calcium, calprotectin is capable of sequestering the transition metals iron, manganese and zinc via chelation. 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 the cytosol of a neutrophil, and it is secreted by an unknown mechanism during inflammation. Faecal calprotectin has been used to detect intestinal inflammation (colitis or enteritis) and can serve as a biomarker for inflammatory bowel diseases. Blood-based calprotectin (in serum and plasma) is used in diagnostics of multiple inflammatory diseases, including autoimmune diseases, like arthritis, and severe infections including sepsis.

== Structure == thumb|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.