NMR spectra and restrained molecular dynamics of the mushroom toxin viroisin

Total Synthesis of Alloviroidin

Alloviroidin is a cyclic heptapeptide, produced by several species of Amanita mushrooms, that demonstrates high affinity for F-actin as is characteristic of virotoxins and phallotoxins. Alloviroidin was synthesized via a [3 + 4] fragment condensation of Fmoc-d-Thr(OTBS)-d-Ser(OTBS)-(2 S,3 R,4 R)-DHPro(OTBS)₂-OH and H-Ala-Trp(2-SO₂Me)-(2 S,4 S)-DHLeu(5-OTBS)-Val-OMe to form bond A. The linear heptapeptide favored a turn conformation, facilitating cyclization between Val¹ and d-Thr² (position B). Global deprotection and HPLC purification afforded alloviroidin with NMR spectra in excellent agreement with the natural product.

Urotensin-II Ligands: An Overview from Peptide to Nonpeptide Structures

Urotensin-II was originally isolated from the goby urophysis in the 1960s as a vasoactive peptide with a prominent role in cardiovascular homeostasis. The identification of human isoform of urotensin-II and its specific UT receptor by Ames et al. in 1999 led to investigating the putative role of the interaction U-II/UT receptor in multiple pathophysiological effects in humans. Since urotensin-II is widely expressed in several peripheral tissues including cardiovascular system, the design and development of novel urotensin-II analogues can improve knowledge about structure-activity relationships (SAR). In particular, since the modulation of the U-II system offers a great potential for therapeutic strategies related to the treatment of several diseases, like cardiovascular diseases, the research of selective and potent ligands at UT receptor is more fascinating. In this paper, we review the developments of peptide and nonpeptide U-II structures so far developed in order to contribute also to a more rational and detectable design and synthesis of new molecules with high affinity at the UT receptor.

Toxins of Amanita phalloides

The most poisonous mushroom toxins are produced by Amanita phalloides (death cap). The occurrence and chemistry of three groups of toxins (amatoxins, phallotoxins and virotoxins) are summarized. The concentration and distribution of toxins in certain species are variable, with the young fruit body containing lower, and the well-developed fungus higher concentrations, but there is a high variability among specimens collected in the same region. Regarding phallotoxins, the volva (the ring) is the most poisonous. The most important biochemical effect of amatoxins is the inhibition of RNA polymerases (especially polymerase II). This interaction leads to a tight complex and the inhibition is of a non-competitive type. Non-mammalian polymerases show little sensitivity to amanitins. The amatoxins cause necrosis of the liver, also partly in the kidney, with the cellular changes causing the fragmentation and segregation of all nuclear components. Various groups of somatic cells of emanation resistance have been isolated, including from a mutant of Drosophila melanogaster. The phallotoxins stimulate the polymerization of G-actin and stabilize the F-actin filaments. The interaction of phallotoxins occurs via the small, 15-membered ring, on the left side of the spatial formula. The symptoms of human poisoning and the changes in toxin concentrations in different organs are summarized. Conventional therapy includes: (1) stabilization of patient's condition with the correction of hypoglycaemia and electrolytes; (2) decontamination; and (3) chemotherapy with different compounds. Finally, certain antagonists and protective compounds are reviewed, bearing in mind that today these have more of a theoretical than a practical role.

Nuclear magnetic resonance studies of the C-terminal human growth hormone fragment I179-C182-[SS]-C189-P191 and the related trisulfide peptide I179-C182-[SSS]-C189-P191

The synthetic C-terminal hGH fragment I179-C182-[SS]-C189-P191 and the related trisulfide peptide I179-C182-[SSS]-C189-P191 have been studied using homonuclear 1H-NMR methods and distance geometry calculations. The 1H-NMR spectra of both the disulfide (diS) and the trisulfide (triS) were completely assigned. Amide proton exchange rates, NOEs and the temperature dependence of the NH chemical shifts indicate a hydrogen bond in triS between Val185 and Ser188 stabilizing a turn in this region. 3JH,H coupling constants and NOEs were measured and used as input for distance geometry calculations. For triS two families of structures with averaged pairwise backbone root mean square deviations for Cys182-Cys189 of 1.3-1.5 A were found, only one of which is compatible with experimental data. For diS only one family of structures was found, but with such a low structural definition (back bone rmsd > 2 A) that no interpretation into a consensus structure is useful. The generated structures were compared to the crystal structure of the terminal loop in hGH, complexed to its binding proteins. The resemblance was low between the solution structures of the tridecapeptides and the terminal hGH loop.