Aspergilli express fusion proteins of an animal haem peroxidase domain with fatty
acid dioxygenase (DOX) activity ( approximately 600 amino acids) and a functional
or non-functional hydroperoxide isomerase/cytochrome P450 domain ( approximately 500
amino acids with EXXR and GPHXCLG motifs). 5,8-Linoleate diol synthases (LDS; ppoA)
and 10R-DOX (ppoC) of Aspergillusnidulans and A. fumigatus belong to this group. Our
objective was to determine the oxylipins formed from linoleic acid by A. clavatus
and their mechanism of biosynthesis. A. clavatus oxidized linoleic acid to (8R)-hydroperoxylinoleic
acid (8R-HPODE), (10R)-hydroperoxy-8(E),12(Z)-octadecadienoic acid (10R-HPODE), and
to (5S,8R)-dihydroxy- and (8R,11S)-dihydroxylinoleic acids (DiHODE) as major products.
This occurred by abstraction of the pro-S hydrogen at C-8 and antarafacial dioxygenation
at C-8 or at C-10 with double bond migration. 8R-HPODE was then isomerized to 5S,8R-DiHODE
and to 8R,11S-DiHODE by abstraction of the pro-S hydrogens at C-5 and C-11 of 8R-HPODE,
respectively, followed by suprafacial oxygenation. The genome of A. clavatus codes
for two enzymes, which can be aligned with >65% amino acid identity to 10R-DOX and
5,8-LDS, respectively. The 5,8-LDS homologue likely forms and isomerizes 8R-HPODE
to 5S,8R-DiHODE. A third gene (ppoB) codes for a protein which carries a serine residue
at the cysteine position of the P450 motif. This Cys to Ser replacement is known to
abolish P450 2B4 catalysis and the hydroperoxide isomerase activity of 5,8-LDS, suggesting
that ppoB of A. clavatus may not be involved in the biosynthesis of 8R,11S-DiHODE.