THAP4 is a nuclear protein containing a C-terminal nitrobindin (Nb) domain that functions as a heme-binding peroxynitrite detoxification enzyme 1. The ferric heme-Fe(III) center catalyzes the conversion of peroxynitrite to nitrate while protecting free L-tyrosine from peroxynitrite-mediated nitration, operating through peroxynitrite isomerase activity 2. THAP4 localizes to both the cytoplasm and nucleus via a nuclear localization sequence, where the N-terminal region possesses transcriptional activity that may be modulated by the C-terminal Nb domain acting as a nitric oxide and peroxynitrite sensor 2. The protein represents an evolutionarily conserved component of cellular antioxidant defenses against reactive nitrogen and oxygen species 2. Clinically, THAP4 is relevant to peripheral T-cell lymphomas (PTCLs), where recurrent gene fusions (VAV1-THAP4) have been identified that drive oncogenic VAV1 activation 34. Additionally, THAP4 loss through 2q37 microdeletion contributes to neurodevelopmental phenotypes including developmental delay, microcephaly, and epilepsy, suggesting a role in cortical and corpus callosum development 5.