Enniatin B and Valinomycin as Ion Carriers: An Empirical Force Field Analysis

Abstract

The alkali-ion binding properties of two natural depsipeptide ion carriers, enniatin B (EnB) and valinomycin (VM), are examined and compared by the empirical force field method. While VM has been shown to bind preferentially K+, Rb+, and Cs+ over Na+ in most solvents, EnB is considerably less specific. We find that EnB forms two kinds of complexes, internal and external. In internal complexes, the ion binds to all six carbonyl oxygens, while in external ones, only three oxygens, preferentially those of the D-hydroxy-isovaleryl residues, are bound. The size of the internal cavity is best suited for Na+, while K+ and Rb+ squeeze in asymmetrically by distorting the molecule, and Cs+ not at all. External binding is much less specific. Since internal complexes possess much higher strain energies than external ones, the latter may be at least as stable as the former, even in fairly non-polar solvents. VM is calculated to bind only internally, and with much less strain energy than EnB. The size of its internal cavity is well suited for binding the ions K+, Rb+, and Cs+, but is too big for Na+. The difference between the binding energies of Na+ and K+ is much smaller than that between the corresponding hydration enthalpies, thus explaining the binding preference for the latter ion.

Optimization of Enniatin Production by Solid-Phase Fermentation of Fusarium tricinctum

“…Due to ionophoric properties, enniatins have been shown to have insecticidal activity as well as antimycobacterial activity, one of the most potent being enniatin B (Ovchinnikov et al, 1974;Lifson et al, 1984;Visconti et al, 1992;Doebler, 2000;Firáková et al, 2007). They inhibit various enzymes, e.g.…”

Study of gas‐phase molecular recognition using Fourier transform ion cyclotron resonance mass spectrometry (FTICR/MS)

“…Perhaps the most famous synthetic recognition agents are the crown ethers, first reported by Pedersen4 in 1967, which selectively bind alkali metal cations in solution, apparently on the basis of cation size. Related hosts include: cryptands,5 which are more rigid, bicyclic versions of the crown ethers with very high metal binding affinities and specificities; calixarenes,6 which are cyclic polyphenols; small biological ionophores such as valinomycin;7 and cyclodextrins,8 cyclic polysaccharides that form inclusion complexes with small organic guests in condensed media. Fundamental studies, such as are discussed here, are important for understanding, on a molecular level, the principles that govern recognition.…”

Experimental and theoretical study on complexation of the ammonium cation with enniatin B

“…They appear in nature as mixtures of cyclic depsipeptides -the main variants are enniatins A, A1, B, and B1, together with minor amounts of enniatins C, D, E, and F. Enniatins function as ionophores by their incorporation into the cellular membrane to form dimeric structures. They transport monovalent ions across the membrane, especially the mitochondrial membranes, affecting oxidative phosphorylation uncoupling [5][6][7][8]. It has been demonstrated that enniatins have a cytotoxic effect on human cancer cells [9].…”