This domain appears to be an SH3 domain of the SH3b2-type, and is the second SH3 domain to be found, downstream of 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 last, the C-terminal region, is the catalytic domain of the cysteine-peptidase type, ie family NLPC_P60, Pfam:PF00877 (details derived from TOPSAN).