Crystallographic analysis of a cupin superfamily enzyme from Microcystis aeruginosa involved in aeruginosin biosynthesis

Aeruginosins are a class of cyanobacteria-derived bioactive linear tetrapeptides composed of nonproteinogenic amino-acid residues, such as the 2-carboxy-6-hydroxyoctahydroindole (Choi) moiety, which is the hallmark of aeruginosin. The biosynthetic pathway of the Choi moiety remains elusive. Previous studies have suggested that AerE, a protein that possesses two cupin domains, participates in the biosynthesis of the Choi moiety. In this study, recombinant AerE from Microcystis aeruginosa, which was overexpressed in Escherichia coli and purified by Ni²⁺-chelating affinity and gel-filtration chromatography, was successfully crystallized and X-ray diffraction analysis was performed. The crystal belonged to the orthorhombic space group P2₁2₁2₁, with unit-cell parameters a = 34.770, b = 62.133, c = 87.401 Å. The diffraction data from the crystal were scaled to a maximum resolution of 1.60 Å. The calculated Matthews coefficient of the crystal is 1.93 Å³ Da^-1, suggesting that there is one molecule in the asymmetric unit.