Antamanide crystal structure

The extremely poisonous green mushroom Amanita phalloides contains a number of cyclic peptides classified as phallotoxins (heptapeptides), ama-toxins (octapeptides), and a decapeptide antagonist called antamanide (Wieland and Wieland, 1972). Crystal structure analyses have been completed on jS-amanitin, on antamanide, and on a biologically active analog, both com-plexed and uncomplexed. 

Valinomycin, a cyclic 12-depsipeptide with the sequence cyc/o(LVal-DHyv-DVal-LLac)3, selectively transports K ions across natural and synthetic membranes. The conformations of the K complex and the uncomplexed form of valinomycin are different, but not as markedly different as the com-plexed and uncomplexed forms of antamanide. The molecular formula of valinomycin exhibits a threefold symmetry, which is maintained in the crystalline state for the K complex. If the differences in the side chains are overlooked, the approximate symmetry is raised to An early crystal structure determination of the KAUCI4 complex (Pinkerton et al, 1969) established that the ion is octahedrally coordinated to the carbonyl oxygen atoms of the six ester groups and that the carbonyl oxygen atoms from the six amide groups form hydrogen bonds with the six NH moieties (4 1 type... 

Antamanide. Antamanide is a cyclic decapeptide which occurs in the Amanita mushroom. Karle has determined and refined the structures of crystals of a complex of antamanide with lithium and of a complex of an analog of antamanide with sodium [37, 38]. Antamanide has a cyclic backbone it contains four proline residues, and four of its oxygens are ligands of the ion. Consequently, the conformation of antamanide is compact and shows a number of nonbonded contacts. The molecule is quite hydrophobic, and the crystal structure forms a hydrophobic matrix of antamanide... 

The rms deviation between the energy-minimized and refined crystal structures is a little over 0.1 A for both molecules. Since the minimizations start with models identical to the refined crystal structures, it is to be expected that the rms deviations increase as the minimizations progress. This is indeed the case. The minimization was not carried out in precisely the same way with both structures, but at a comparable stage of energy minimization the rms error is about 0.03 A greater for sodium antamanide analog than for lithium antamanide. 

Karle IL (1986) Water structure in [Phe4 Ala4] antamanide 12H20 crystallized from diox-ane. Int J Pept Protein Res 28 6-12... 

Antamanide is a lipophilic neutral compound that forms colorless crystals which are easily soluble in alcohols but almost insoluble in water it has a molecular mass of 1147 (mass spectroscopy). On hydrolysis, antamanide is spHt to yield the L-amino acids alanine, valine, phenylalanine, proline in a molar ratio of 1 1 4 4. Its structure, determined by gas chromatographic separation of the fragments obtained by partial methanolysis and their analysis by mass spectroscopy is displayed in Fig. 17. 

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