An unusual carbon–carbon bond cleavage reaction during phosphinothricin biosynthesis

Abstract

The phosphinothricin tripeptide (PTT) is a naturally occurring compound that contains a phosphorous-carbon bond. The biosynthesis of PTT involves the conversion of hydroxyethylphosphonate (HEP) to hydroxymethylphosphonate (HMP). The enzyme responsible for this chemical transformation (hydroxyethylphosphonate dioxygenase or HEPD) is a mononuclear non-haem iron(II)-dependent dioxygenase, and it catalyses the cleavage of a C(sp3)–C(sp3) bond. Here Robert Cicchillo and colleagues solve the X-ray crystal structure of HEPD and biochemically explore the mechanism of this remarkable transformation. The biosynthesis of the naturally occurring compound phosphinothricin tripeptide (PTT) involves the conversion of 2-hydroxyethylphosphonate (HEP) to hydroxymethylphosphonate (HMP). This requires the cleavage of a C(sp3)–C(sp3) bond. Here, the X-ray crystal structure of the enzyme that catalyzes this reaction (hydroxyethylphosphonate dioxygenase, HEPD) is solved, and the mechanism of this remarkable transformation is explored. Natural products containing phosphorus–carbon bonds have found widespread use in medicine and agriculture1. One such compound, phosphinothricin tripeptide, contains the unusual amino acid phosphinothricin attached to two alanine residues. Synthetic phosphinothricin (glufosinate) is a component of two top-selling herbicides (Basta and Liberty), and is widely used with resistant transgenic crops including corn, cotton and canola. Recent genetic and biochemical studies showed that during phosphinothricin tripeptide biosynthesis 2-hydroxyethylphosphonate (HEP) is converted to hydroxymethylphosphonate (HMP)2. Here we report the in vitro reconstitution of this unprecedented C(sp3)–C(sp3) bond cleavage reaction and X-ray crystal structures of the enzyme. The protein is a mononuclear non-haem iron(ii)-dependent dioxygenase that converts HEP to HMP and formate. In contrast to most other members of this family, the oxidative consumption of HEP does not require additional cofactors or the input of exogenous electrons. The current study expands the scope of reactions catalysed by the 2-His–1-carboxylate mononuclear non-haem iron family of enzymes.