The S100 family protein MRP‐14 (S100A9) has homology with the contact domain of high molecular weight kininogen

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Abstract
The heterodimeric molecule MRP‐8/MRP‐14 (S100A8/S100A9) is abundantly expressed in circulating monocytes and neutrophils. We report here an homology between the C‐terminal ‘tail’ region of MRP‐14 (S100A9) and sequences within the plasma protein, high molecular weight kininogen (HMWK) which are involved in binding to negatively charged surfaces such as kaolin. MRP‐14 also binds to kaolin and is competitively inhibited by HMWK and by peptides corresponding to MRP‐14 tail and the HMWK ‘contact’ regions. Furthermore both MRP‐14 and the tail peptide inhibit the coagulation cascade in vitro giving functional relevance to the homology between MRP‐14 and HMWK. At inflammatory sites, MRP‐8/14 is localised to areas of close contact between myeloid cells and endothelium. The results of this study identify a potential binding region in MRP‐14 and suggest that it could function by interfering with fibrin formation at sites of leukocyte transendothelial migration.