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Pathogenic organisms may be sensitive to inhibitors of sterol biosynthesis, which carry antimetabolite properties, through manipulation of the key enzyme, sterol methyltransferase (SMT). Here, we isolated natural suicide substrates of the ergosterol biosynthesis pathway, cholesta-5,7,22,24-tetraenol (CHT) and ergosta-5,7,22,24(28)-tetraenol (ERGT), and demonstrated their interference in Acanthamoeba castellanii steroidogenesis: CHT and ERGT inhibit trophozoite growth (EC50 of 51 nM) without affecting cultured human cell growth. Washout experiments confirmed that the target for vulnerability was SMT. Chemical, kinetic, and protein-binding studies of inhibitors assayed with 24-AcSMT [catalyzing C28-sterol via Δ24(28)-olefin production] and 28-AcSMT [catalyzing C29-sterol via Δ25(27)-olefin production] revealed interrupted partitioning and irreversible complex formation from the conjugated double bond system in the side chain of either analog, particularly with 28-AcSMT. Replacement of active site Tyr62 with Phe or Leu residues involved in cation-π interactions that model product specificity prevented protein inactivation. The alkylating properties and high selective index of 103 for CHT and ERGT against 28-AcSMT are indicative of a new class of steroidal antibiotic that, as an antimetabolite, can limit sterol expansion across phylogeny and provide a novel scaffold in the design of amoebicidal drugs. Animal studies of these suicide substrates can further explore the potential of their antibiotic properties.

The sterol metabolome of Acanthamoeba castellanii (Ac) yielded 25 sterols. Substrate screening of cloned AcCYP51 revealed obtusifoliol as the natural substrate which converts to Δ(8,14)-sterol (

The paper addresses wave motions in an unbounded sandwich plate with and without heavy fluid loading in a plane problem formulation. A sandwich plate is composed of two identical isotropic skin plies and an isotropic core ply. Several alternative theories for stationary dynamics of such a plate or a beam are derived, including a formulation in the framework of a theory of elasticity applied for a core ply. ‘In-phase’ and ‘anti-phase’ wave motions (with respect to transverse deflections of skins) of a sandwich beam are analyzed independently of each other. Dispersion curves obtained by the use of ‘elementary’ theories are compared with those obtained by the use of an ‘exact’ theory (which involves the theory of elasticity in a description of wave motion in a core ply) for a plate without fluid loading. It is shown that these simplified models are capable of giving a complete and accurate description of all propagating waves in not too high-frequency range, which is sufficient in practical naval and aerospace engineering. In the case of heavy fluid loading, similar analysis is performed for ‘anti-phase’ wave motions of a beam. Two simplified theories as well as an ‘exact’ one are extended to capture fluid loading effects. A good agreement between results obtained in ‘elementary’ and ‘exact’ problem formulations is demonstrated. The role of fluid's compressibility in the generation of propagating waves in a sandwich plate is explored. It is shown that, whereas analysis of wave motions in the case of an incompressible fluid predicts an existence of two propagating waves, only one such wave exists when a fluid is sufficiently compressible. The threshold magnitude of the ratio of a sound speed in an acoustic medium to a sound speed in a skin's material is found, which separates these two regimes of wave motions for a given set of parameters of sandwich plate composition.