This domain, at the N-terminus, appears to be the stabilising domain for the structure from Swiss:Q72DN3, PDB:3m1u, which is a four-domain protein. The next domain is an SH3b1, the third an SH3b2 and the last, the C-terminal region, the catalytic domain of the cysteine-peptidase type, ie family NLPC_P60, Pfam:PF00877 (details derived from TOPSAN).