posted on 2024-02-22, 18:37authored byLi Li, Weimao Zhong, Hang Liu, Patricia Espinosa-Artiles, Ya-ming Xu, Chen Wang, Jose Manuel Verdugo Robles, Tiago Antunes Paz, Marielle Cascaes Inácio, Fusheng Chen, Yuquan Xu, A. A. Leslie Gunatilaka, István Molnár
Polyketides
with the isochroman-3-one pharmacophore are rare among
fungal natural products as their biosynthesis requires an unorthodox
S-type aromatic ring cyclization. Genome mining uncovered a conserved
gene cluster in select leotiomycetous fungi that encodes the biosynthesis
of cytosporones, including isochroman-3-one congeners. Combinatorial
biosynthesis in total biosynthetic and biocatalytic formats in Saccharomyces cerevisiae and in vitro reconstitution
of key reactions with purified enzymes revealed how cytosporone structural
and bioactivity diversity is generated. The S-type acyl dihydroxyphenylacetic
acid (ADA) core of cytosporones is assembled by a collaborating polyketide
synthase pair. Thioesterase domain-catalyzed transesterification releases
ADA esters, some of which are known Nur77 modulators. Alternatively,
hydrolytic release allows C6 hydroxylation by a flavin-dependent monooxygenase,
yielding a trihydroxybenzene moiety. Reduction of the C9 carbonyl
by a short chain dehydrogenase/reductase initiates isochroman-3-one
formation, affording cytosporones with cytotoxic and antimicrobial
activity. Enoyl di- or trihydroxyphenylacetic acids are generated
as shunt products, while isocroman-3,4-diones are formed by autoxidation.
The cytosporone pathway offers novel polyketide biosynthetic enzymes
for combinatorial synthetic biology to advance the production of “unnatural”
natural products for drug discovery.