Structure, Function, and Inhibition of Staphylococcus aureus Heptaprenyl Diphosphate Synthase

Graphical Abstract

New drug target: Staphylococcus aureus heptaprenyl diphosphate synthase (HepPPS), involved in menaquinone biosynthesis, functions as a heterodimer and is inhibited by bisphosphonates (IC₅₀=0.83 μm), which also inhibit S. aureus cell growth, an effect that is rescued by menaquinone. HepPPS is also partially inhibited by its substrates FPP as well as IPP, most likely due to disruption of the heterodimeric complex structure.

Abstract

We report the first structure of heptaprenyl diphosphate synthase from Staphylococcus aureus (SaHepPPS), together with an investigation of its mechanism of action and inhibition. The protein is involved in the formation of menaquinone, a key electron transporter in many bacteria, including pathogens. SaHepPPS consists of a “catalytic ” subunit (SaHepPPS-2) having two “DDXXD” motifs and a “regulatory” subunit (SaHepPPS-1) that lacks these motifs. High concentrations of the substrates, isopentenyl diphosphate and farnesyl diphosphate, inhibit the enzyme, which is also potently inhibited by bisphosphonates. The most active inhibitors (K_i∼200 nm) were N-alkyl analogues of zoledronate containing ∼C₆ alkyl side chains. They were modestly active against S. aureus cell growth, and growth inhibition was partially “rescued” by the addition of menaquinone-7. Because SaHepPPS is essential for S. aureus cell growth, its structure is of interest in the context of the development of menaquinone biosynthesis inhibitors as potential antibiotic leads.