This domain appears to be an SH3 domain of the SH3b1-type, and is just C-terminal to an N-terminal domain that is probably the stabilising domain for the structure from Swiss:Q72DN3, PDB:3m1u, which is a four-domain protein. The next domain is an SH3b2 and the last, the C-terminal region, is the catalytic domain of the cysteine-peptidase type, ie family NLPC_P60, Pfam:PF00877 (details derived from TOPSAN).