Expression, purification, crystallization and preliminary X-ray analysis of para-nitrophenol 4-monooxygenase from Pseudomonas putida DLL-E4

Para-nitrophenol 4-monooxygenase (PnpA) plays an important role in bacterial degradation of para-nitrophenol by oxidative release of the nitro group from the aromatic ring to form p-benzoquinone. In order to understand the structural basis of the function of this enzyme, PnpA was cloned, expressed in Escherichia coli and purified. PnpA was crystallized by the hanging-drop vapour-diffusion technique with PEG 4000 as precipitant. The PnpA crystals belonged to space group P2₁2₁2₁, with unit-cell parameters a = 54.47, b = 77.56, c = 209.17 Å, and diffracted to 2.24 Å resolution.