Discovery of a new P450 enzyme DkpdB for cyclo(Trp-Phe) dimerization in the marine strain Aspergillus sydowii MNP-2.

Diketopiperazine (DKP) dimers are one of the important microbial natural products owing to their structural diversity and a broad spectrum of biological properties. However, few studies on fungal P450-catalyzed DKP dimerization have been reported. Herein, a novel cytochrome P450 monooxygenase DkpdB was originally discovered in the marine-derived fungus Aspergillus sydowii MNP-2 and shown to catalyze the formation of the DKP dimer WIN 64821 from cyclo(Trp-Phe) through a proposed C3-C3' oxidative coupling reaction. Heterologous expression in Aspergillus nidulans RJMP1.5 together with in vivo and yeast microsomal assays confirmed this activity, and its substrate-binding mode is predicted by structural modeling and molecular docking analyses. Furthermore, site-directed mutagenesis identified E180 and T181 as critical residues for DkpdB-catalyzed dimerization of cyclo(Trp-Phe) by molecular docking. These findings provide new insights into fungal P450-catalyzed DKP dimerization and expand the repertoire of functionally characterized fungal P450 dimerases.