Evidence for radical-mediated catalysis by HppE: a study using cyclopropyl and methylenecyclopropyl substrate analogues. Academic Article uri icon

abstract

  • (S)-2-Hydroxypropylphosphonic acid epoxidase (HppE) is an unusual mononuclear iron enzyme that catalyzes the oxidative epoxidation of (S)-2-hydroxypropylphosphonic acid ((S)-HPP) in the biosynthesis of the antibiotic fosfomycin. HppE also recognizes (R)-2-hydroxypropylphosphonic acid ((R)-HPP) as a substrate and converts it to 2-oxo-propylphosphonic acid. To probe the mechanisms of these HppE-catalyzed oxidations, cyclopropyl- and methylenecyclopropyl-containing compounds were synthesized and studied as radical clock substrate analogues. Enzymatic assays indicated that the (S)- and (R)-isomers of the cyclopropyl-containing analogues were efficiently converted to epoxide and ketone products by HppE, respectively. In contrast, the ultrafast methylenecyclopropyl-containing probe inactivated HppE, consistent with a rapid radical-triggered ring-opening process that leads to enzyme inactivation. Taken together, these findings provide, for the first time, experimental evidence for the involvement of a C2-centered radical intermediate with a lifetime on the order of nanoseconds in the HppE-catalyzed oxidation of (R)-HPP.

author list (cited authors)

  • Huang, H., Chang, W., Pai, P., Romo, A., Mansoorabadi, S. O., Russell, D. H., & Liu, H

complete list of authors

  • Huang, Hui||Chang, Wei-chen||Pai, Pei-Jing||Romo, Anthony||Mansoorabadi, Steven O||Russell, David H||Liu, Hung-wen

publication date

  • January 1, 2015 11:11 AM