Mouse SWAM1 and SWAM2 are antibacterial proteins composed of a single whey acidic protein motif

Antibacterial proteins are important participants in the innate immunity system. Elafin and SLPI are the whey acidic protein (WAP) motif proteins with both antibacterial activity and antiprotease activity, and their role in innate immunity is under intense investigation. We cloned two novel antibacterial WAP motif proteins from mice, SWAMI and SWAM2. SWAMI and SWAM2 are composed of a signal sequence and a single WAP motif that has high homologies with the WAP motifs of elafin and SLPI. SWAMI is constitutively expressed in kidney and epididymis, and is induced in the pneumonic lung. SWAM2 is constitutively expressed in tongue. SWAMI and SWAM2 inhibit the growth of both Escherichia coli and Staphylococcus aureus at a IC90 (concentration that achieves 90% inhWition) of 10 muM. Human gems LOC149709 and huWAP2 are considered to be human SWAMI and SWAM2, respectively. These and several WAP motif proteins (WAP1, elafin, SLPI, HE4, eppin, C20orf170, LOC164237, and WFDC3) form a gene cluster on human chromosome 20, suggesting that they may be derived from the same ancestral gene by gene duplication. Our results underscore the role of the WAP motif as a skeletal motif to form antibacterial proteins, and warrant the study of antibacterial activity in other WAP motif proteins.