OX4 Is an NADPH-Dependent Dehydrogenase Catalyzing an Extended Michael Addition Reaction To Form the Six-Membered Ring in the Antifungal HSAF
Year: 2019
Type: article
Abstract: The polycyclic tetramate macrolactam HSAF is an antifungal natural product isolated from Lysobacter enzymogenes . HSAF and its analogues have a distinct chemical structure and new mode of antifungal action. The mechanism by which the 5/5/6 tricycle of HSAF is formed from the polyene precursor is not totally clear. Here, we used purified OX4, a homologous enzyme of alcohol dehydrogenase/Zn-binding proteins, to show the enzymatic mechanism for six-membered ring formation. The results from the deuterium isotope incorporation demonstrated that OX4 selectively transfers the pro - R hydride of NADPH to C21 and one proton from water to C10 of 3-deOH alteramide C ( 1 ), resulting in 3-deOH HSAF ( 2 ) through a reductive cyclization of the polyene precursor by a mechanism consistent with an extended 1,6-Michael addition reaction. The regioselective incorporation of the NADPH hydride into C21 of 1 is also stereoselective, leading to the 21 S configuration of 2 . This work represents the first characterization of the activity and selectivity of the enzyme for six-membered ring formation in a group of distinct antifungal polycyclic tetramate macrolactams.
Source: Biochemistry
Language: English
Subfield: Pharmacology
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W2942849976