This domain was first characterised as the C-terminal domain of Pab87 serine protease from Pyrococcus abyssi [1]. The domain is reported to play a crucial role in Pab87 octamerisation and active site compartmentalisation. Its up-and-down 8-stranded beta-barrel 3D structure is reminiscent of the one found in lipocalins.

1: Structure of the archaeal pab87 peptidase reveals a novel self-compartmentalizing protease family. Delfosse V, Girard E, Birck C, Delmarcelle M, Delarue M, Poch O, Schultz P, Mayer C; PLoS One. 2009;4:e4712. PMID:19266066