Structural basis of a 2-oxoglutarate-dependent heme-oxygenase-like enzyme HamA in fragin biosynthesis.

The fungicide fragin, which contains a diazeniumdiolate moiety, exhibits a broad spectrum of biological activities. HamA, the key enzyme responsible for forming the nitrogen-nitrogen bond in this moiety, was investigated in this study. We determined the crystal structure of HamA at 2.0 Å resolution, revealing a mononuclear iron center in the active site coordinated by both the "2His-1Glu" motif and an acetate group. Notably, HamA adopts a heme oxygenase-like fold, forming a hydrophobic cavity within a helical bundle that likely accommodates the substrate. Structural data confirmed the presence of an acetate and a formate group near the active site and microscale thermophoresis (MST) experiments further demonstrated HamA's ability to bind 2-oxoglutarate (2OG) with a dissociation constant (K d) of 208 ± 1.42 μM. In summary, this study elucidates the 2OG-dependent heme-oxygenase-like enzyme HamA with a monoiron active center, providing critical structural insights into the mechanistic formation of the diazeniumdiolate moiety in fragin.