Phosphoenolpyruvate Mutase-Catalyzed C-P Bond Formation: Mechanistic Ambiguities and Opportunities.

Phosphonates are produced across all domains of life and used widely in medicine and agriculture. Biosynthesis almost universally originates from the enzyme phosphoenolpyruvate mutase (Ppm), EC 5.4.2.9, which catalyzes O-P bond cleavage in phosphoenolpyruvate (PEP) and forms a high energy C-P bond in phosphonopyruvate (PnPy). Mechanistic scrutiny of this unusual intramolecular O-to-C phosphoryl transfer began with the discovery of Ppm in 1988 and concluded in 2008 with computational evidence supporting a concerted phosphoryl transfer via a dissociative metaphosphate-like transition state. This mechanism deviates from the standard 'in-line attack' paradigm for enzymatic phosphoryl transfer that typically involves a phosphoryl-enzyme intermediate, but definitive evidence is sparse. Here we review the experimental evidence leading to our current mechanistic understanding and highlight the roles of previously underappreciated conserved active site residues. We then identify remaining opportunities to evaluate overlooked residues and unexamined substrates/inhibitors.