The newly discovered bacterial phosphothreonine lyases perform a post-translational modification of host cell signaling proteins through a novel catalytic mechanism that irreversibly removes the phosphate group from a phosphorylated threonine via beta-elimination. This "eliminylation" reaction is shown by ab initio QM/MM studies to proceed via an E1cB-like pathway, in which the carbanion intermediate is stabilized by an enzyme oxyanion hole provided by Lys104 and Tyr158 of SpvC.