Bifunctional CYP81AA proteins catalyse identical hydroxylations but alternative regioselective phenol couplings in plant xanthone biosynthesis.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 27145837.
- Also identified by DOI 10.1038/ncomms11472 and PMC identifier 4858744.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Xanthones are natural products present in plants and microorganisms. In plants, their biosynthesis starts with regioselective cyclization of 2,3',4,6-tetrahydroxybenzophenone to either 1,3,5- or 1,3,7-trihydroxyxanthones, catalysed by cytochrome P450 (CYP) enzymes. Here we isolate and express CYP81AA-coding sequences from Hypericum calycinum and H. perforatum in yeast. Microsomes catalyse two consecutive reactions, that is, 3'-hydroxylation of 2,4,6-trihydroxybenzophenone and C-O phenol coupling of the resulting 2,3',4,6-tetrahydroxybenzophenone. Relative to the inserted 3'-hydroxyl, the orthologues Hc/HpCYP81AA1 cyclize via the para position to form 1,3,7-trihydroxyxanthone, whereas the paralogue HpCYP81AA2 directs cyclization to the ortho position, yielding the isomeric 1,3,5-trihydroxyxanthone. Homology modelling and reciprocal mutagenesis reveal the impact of S375, L378 and A483 on controlling the regioselectivity of HpCYP81AA2, which is converted into HpCYP81AA1 by sextuple mutation. However, the reciprocal mutations in HpCYP81AA1 barely affect its regiospecificity. Product docking rationalizes the alternative C-O phenol coupling reactions. Our results help understand the machinery of bifunctional CYPs.
Medical subject headings
- Cytochrome P-450 Enzyme System
- Hypericum
- Phenol
- Plant Proteins
- Xanthones