This is the C-terminal domain of HOIP present in Homo sapiens. HOIP synthesize the linear ubiquitin chains that help control innate immunity and inflammation. This region has an RBR domain which catalyzes the transfer of ubiquitin onto a substrate [1].

1: Structural basis for ligase-specific conjugation of linear ubiquitin chains by HOIP. Stieglitz B, Rana RR, Koliopoulos MG, Morris-Davies AC, Schaeffer V, Christodoulou E, Howell S, Brown NR, Dikic I, Rittinger K; Nature. 2013;503:422-426. PMID:24141947