This is a bacterial domain which has been named BsuPI in Bacillus subtilis. This domain is found in Swiss:P39804, where it has been suggested to regulate the major intracellular proteinase (ISP-1) activity in vivo [1]. The structure of proteins in this family adopt an Ig-like fold [2].

1: Characterization of the gene encoding an intracellular proteinase inhibitor of Bacillus subtilis and its role in regulation of the major intracellular proteinase. Shiga Y, Yamagata H, Udaka S; J Bacteriol. 1993;175:7130-7137. PMID:8226659

2: The first structure in a family of peptidase inhibitors reveals an unusual Ig-like fold. Rigden DJ, Xu Q, Chang Y, Eberhardt RY, Finn RD, Rawlings ND; F1000Res. 2013;2:154. PMID:24555072