Antimicrobial proteins with homology to serine proteases.

The azurophil granule, a specialized lysosome of human neutrophils, contains a family of antimicrobial proteins with structural homology to serine proteases, the serprocidins. Three members of this family are serine proteases (cathepsin G, elastase and proteinase-3) and one is a proteolytically inactive homologue (azurocidin). They are synthesized as preproproteins with a characteristic leader peptide and a propiece, both of which are removed by processing enzymes to yield the mature protein. The functional genes for three serprocidins (elastase, proteinase-3 and azurocidin) are grouped in a single genetic locus on chromosome 19 and are coordinately expressed and regulated during haemopoietic differentiation. Multiple and sometimes overlapping biological functions are a feature of this family, yet they all seem to pertain to host immunity. The structural requirements for the function of one member of this group (azurocidin), particularly its antibiotic function, are under investigation.