The toxic peptides from Amanita mushrooms

Alloviroidin, the naturally occurring toxic isomer of the cyclopeptide viroidin

A novel toxic cyclopeptide from Amanita suballiacea (Murr.) mushrooms that possesses structural features similar to viroidin is described. This peptide, alloviroidin, is identical with viroidin in mass, affinity for actin, and all amino acids except for one. The single discernible difference between the two peptides exists in the configuration at carbon 4 of the 4,5-dihydroxyleucine residues, as shown by a combination of chemical modification and magnetic resonance experiments. The configuration of this residue in viroidin is similar to that of phalloidin and is 2S,4R, while that in alloviroidin is established to be 2S,4S. This peptide is thus unique in its hydroxylation pattern among both the virotoxins and phallotoxins and may be an intermediate for more highly hydroxylated virotoxins, such as viroisin.

Synthetic amatoxin analogue. A two-dimensional proton NMR study of S-deoxy-(Ile3)-(D-Ala7)-amaninamide

The effect of substitution of L and D amino acids in amatoxin analogues is discussed in this paper. The structure of the analog where D-alanine substitutes for glycine in position 7 has been worked out in solution by two-dimensional NMR methods using a 500 MHz instrument. The combined use of COSY and NOESY two-dimensional spectra allows a clear assignment of the resonances. The use of the coupling constants permits the calculation of the phi angles of the backbone. The NOE effects reveal the through-space contacts between protons of different peptide units, thus determining the rigidity of the amatoxin structure. On these grounds it has been possible to elucidate the conformation of the amatoxin analogue that resembles very closely that of beta-amanitin, thus explaining the high inhibitory activity toward RNA polymerase B.

Determination of alpha-amanitin and beta-amanitin in human biological fluids by high-performance liquid chromatography

A high-performance liquid chromatographic assay of alpha-amanitin and beta-amanitin in human serum, urine, or stomach washings is described. Sample preparation involves a chemical step with deproteinization and organic solvent treatment, and a selective cleanup and concentration step on reversed-phase prepacked cartridges. Separations are performed on a reversed-phase analytical column under isocratic conditions with uv detection at 280 nm. The method allows the quantitation of alpha- and beta-amanitin separately with a detection limit of 10 ng/ml for both toxins.

Identity of hepatic membrane transport systems for bile salts, phalloidin, and antamanide by photoaffinity labeling

Phalloidin, a bicyclic heptapeptide, and antamanide, a monocyclic decapeptide from the poisonous mushroom Amanita phalloides, interact with bile-salt-binding polypeptides of the hepatocyte membrane, as demonstrated by photoaffinity labeling using the photolabile bile salt derivative 7,7,-azo-3 alpha, 12 alpha-dihydroxy-5 beta-cholan-24-oic acid, either unconjugated or taurine conjugated. With the photolabile derivatives of phalloidin, N-delta-(4-[(1-azi-2,2,2-trifluoroethyl) benzoyl]-beta-alanyl)-delta-aminophalloin, (N epsilon-[4-(1-azi-2,2,2-trifluoroethyl)benzoyl]lys6)-anta manide, the same membrane polypeptides with apparent MrS of 54,000 and 48,000 were labeled as with the photolabile derivatives of unconjugated and conjugated bile salts. The presence of bile salts decreased markedly the extent of labeling of these phalloidin- and antamanide-binding polypeptides. These results indicate that hepatic uptake systems for bile salts, phallotoxins, and the cycloamanide antamanide are identical, thus explaining the organotropism of phallotoxins.

X-ray crystallography of peptides: the contributions of the Italian laboratories

The review article summarizes the most relevant solid state structural and conformational results obtained in the laboratories involved in Italy in the studies of synthetic and natural peptides by x-ray diffraction analyses. Some of the topics will include research studies carried out in other European countries, whereas in other cases studies carried out in Italy will be included in other review articles included in this volume. The review deals with peptides containing symmetrically achiral and unsymmetrically chiral C alpha,alpha-dialkylated glycine residues, peptides containing beta-alanine residues, alpha,beta-dehydroamino acid residues, and aminosuccinyl residues, peptides containing the thioamide surrogate, heterochiral peptides and several bioactive peptides systems with the proposed relationships between function and structure.