This domain is currently only found in a small set of S. coelicolor secreted proteins. There are four conserved cysteines that probably form two disulphide bonds. Proteins 2SCK31.15C (Swiss:Q9ADK5) and SCO3675 (Swiss:Q9X8V7) also have probable beta-propellers at their C-termini. This family includes Swiss:P01077 a known peptidase inhibitor of known structure. This protein has a crystallin like fold Pfam:PF00030 and is distantly related by sequence. It is not known whether other members of this family are peptidase inhibitors.

1: New Knowledge from Old: In silico discovery of novel protein domains in Streptomyces coelicolor. Yeats C, Bentley S, Bateman A; BMC Microbiol 2003;3:3-3. PMID:12625841

2: NMR structure of the Streptomyces metalloproteinase inhibitor, SMPI, isolated from Streptomyces nigrescens TK-23: another example of an ancestral beta gamma-crystallin precursor structure. Ohno A, Tate S, Seeram SS, Hiraga K, Swindells MB, Oda K, Kainosho M; J Mol Biol 1998;282:421-433. PMID:9735297