The effect of triton concentration on the activity of undecaprenyl pyrophosphate synthase inhibitors.

Undecaprenyl pyrophosphate synthase (UPPS) catalyzes the consecutive condensation of 8 molecules of isopentenyl pyrophosphate with farnesyl pyrophosphate to yield C55-undecaprenyl pyrophosphate, which is required for bacterial cell wall synthesis. UPPS is found in both gram-positive and gram-negative bacteria, and based on the differences between bacterial variants of UPPS and their human counterpart, dolicopyrophosphate synthase, it was identified as an attractive antibacterial target. An assay, which monitors the release of Pi by coupling the UPPS catalyzed reaction with inorganic pyrophosphatase, was employed to conduct an HTS campaign using an inhouse collection of compounds. A direct assay measuring the incorporation of 14C-IPP (isopentenyl pyrophosphate) was used as a secondary assay to evaluate the high-throughput screening (HTS) hits. From the HTS campaign, a few classes of UPPS inhibitors were identified. During the process of hit evaluation by the direct assay, the authors observed that Triton, an essential factor for the enzyme activity and accurate formation of the natural product, dramatically altered the inhibitory activity of a particular class of compounds. Above its critical micellar concentration (CMC), Triton abolished the inhibitory activity of these compounds. Further research will be required to establish the biophysical phenomenon that causes this effect. Meanwhile, it can be speculated that Triton (and other detergents) above CMC may hinder the identification in screening compounds of certain classes of hits.