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

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.