A structural model of PpoA derived from SAXS-analysis—Implications for substrate conversion

  • a Georg-August-University, Albrecht-von-Haller-Institute, Department of Plant Biochemistry, Justus-von-Liebig-Weg 11, D-37077 Goettingen, Germany
  • b EMBL Hamburg, BioSAXS group, Notkestrasse 85, D-22603 Hamburg, Germany
  • c Max-Plank-Institute for Biophysical Chemistry, Research group Electron Paramagnetic Resonance, Am Fassberg 11, D-37077 Goettingen, Germany
  • d Georg-August-University, Institute for Microbiology and Genetics, Griesebachstr. 8, D-37077 Goettingen, Germany
  • e Georg-August-University, Institute for Organic and Biomolecular Chemistry, Tammannstrasse 2, D-37077 Göttingen, Germany
  • f University of Hamburg, Centre for Bioinformatics, Bundesstrasse 43, D-20146, Hamburg, Germany


PpoA consists of two domains that form a trimeric structure with a triangular shape.

Dipolar couplings between spins of the monomers support the assignment of Tyr374 as solely radical-site.

Two phenylalanines in the cytochrome P450-domain modulate the specificity of hydroperoxy fatty acid rearrangement.


In plants and mammals, oxylipins may be synthesized via multi step processes that consist of dioxygenation and isomerization of the intermediately formed hydroperoxy fatty acid. These processes are typically catalyzed by two distinct enzyme classes: dioxygenases and cytochrome P450 enzymes. In ascomycetes biosynthesis of oxylipins may proceed by a similar two-step pathway. An important difference, however, is that both enzymatic activities may be combined in a single bifunctional enzyme. These types of enzymes are named Psi-factor producing oxygenases (Ppo). Here, the spatial organization of the two domains of PpoA from Aspergillus nidulans was analyzed by small-angle X-ray scattering and the obtained data show that the enzyme exhibits a relatively flat trimeric shape. Atomic structures of the single domains were obtained by template-based structure prediction and docked into the enzyme envelope of the low resolution structure obtained by SAXS. EPR-based distance measurements between the tyrosyl radicals formed in the activated dioxygenase domain of the enzyme supported the trimeric structure obtained from SAXS and the previous assignment of Tyr374 as radical-site in PpoA. Furthermore, two phenylalanine residues in the cytochrome P450 domain were shown to modulate the specificity of hydroperoxy fatty acid rearrangement.


  • AOS, allene oxide synthase;
  • DEER, double electron–electron resonance;
  • DES, divinyl ether synthase;
  • DiHODE, dihydroxy linoleic acid;
  • DiHOME, dihydroxy oleic acid;
  • Dmax, maximal particle dimension;
  • DOX, dioxygenase;
  • EPR, electron paramagnetic resonance;
  • Et2O, diethyl ether;
  • HPL, hydroperoxide lyase;
  • H(P)ODE, hydro(pero)xy linoleic acid;
  • KODE, oxo-linoleic acid;
  • KOME, oxo-oleic acid;
  • LOX, lipoxygenase;
  • MALDI-TOF, matrix-assisted laser desorption/ionization-time of flight;
  • MW, molecular weight;
  • PGIS, prostacyclin synthase;
  • psi, precocious sexual inducer;
  • Ppo, psi-factor producing oxygenase;
  • PGHS, prostaglandin endoperoxide synthase;
  • Rg, radius of gyration;
  • SAXS, small-angle X-ray scattering;
  • TXAS, thromboxane synthase;
  • Vp, particle volume


  • Cytochrome P450;
  • Dioxygenase;
  • Double electron–electron resonance;
  • Oxylipin;
  • Psi-factor producing oxygenase;
  • Small-angle X-ray scattering