This family contains the N-terminal domain of pirin, a nuclear protein that is highly conserved among mammals, plants, fungi, and prokaryotes. It is widely expressed in dot-like subnuclear structures in human tissues such as liver and heart. Pirin functions as both a transcriptional cofactor and an apoptosis-related protein in mammals and is involved in seed germination and seedling development in plants. The pirins have been assigned as a subfamily of the cupin superfamily based on structure and sequence similarity. The pirins have two tandem cupin-like folds but the C-terminal cupin fold has diverged considerably and does not have a metal binding site. The exact functions of pirins are unknown but they have quercitinase activity in Escherichia coli and are thought to play important roles in transcription and apoptosis. Proteins in this family belong to the cupin superfamily with a conserved "jelly roll-like" beta-barrel fold generally capable of homodimerization.
Jiyao W et al.(2023). "The conserved domain database in 2023.",