This is the N-terminal domain of the alpha subunit, known as PnpD, of Hydroquinone 1,2-dioxygenase (PnpCD) present in Pseudomonas sp. strain WBC-3. PnpCD is the key enzyme in the degradation pathway of pollutant para-nitrophenol (PNP). The N-terminal domain residues Trp-76 and Phe-79 are indispensable in the formation of the active site pocket. The N-terminal domain also plays a vital role in formation of the heterotetrameric structure. Structural homologs of the N-terminal domain exhibit the nature to bind nucleic acids but due to the steric effect of the C-terminal domain, this N-terminal domain cannot bind nucleic acids [1].

1: Crystal structure of PnpCD, a two-subunit hydroquinone 1,2-dioxygenase, reveals a novel structural class of Fe2+-dependent dioxygenases. Liu S, Su T, Zhang C, Zhang WM, Zhu D, Su J, Wei T, Wang K, Huang Y, Guo L, Xu S, Zhou NY, Gu L; J Biol Chem. 2015;290:24547-24560. PMID:26304122