Crystal structure of human pirin: an iron-binding nuclear protein and transcription cofactor.

Pirin is a newly identified nuclear protein that interacts with the oncoprotein B-cell lymphoma 3-encoded (Bcl-3) and nuclear factor I (NFI). The crystal structure of human Pirin at 2.1-A resolution shows it to be a member of the functionally diverse cupin superfamily. The structure comprises two beta-barrel domains, with an Fe(II) cofactor bound within the cavity of the N-terminal domain. These findings suggest an enzymatic role for Pirin, most likely in biological redox reactions involving oxygen, and provide compelling evidence that Pirin requires the participation of the metal ion for its interaction with Bcl-3 to co-regulate the NF-kappaB transcription pathway and the interaction with NFI in DNA replication. Substitution of iron by heavy metals thus provides a novel pathway for these metals to directly influence gene transcription. The structure suggests an interesting new role of iron in biology and that Pirin may be involved in novel mechanisms of gene regulation.