Synthesis and bioactivity of nobilamide B.

An alternative and facile solution/solid-phase approach is reported for the total synthesis of neuroactive peptide, nobilamide B. Z-Dhb was formed in solution via EDC/CuCl induced elimination. The solid-phase synthesis employed HBTU/Oxyma Pure™ coupling using Barlos resin. Synthetic nobilamide B was also found to be neuroactive in primary cultures of dorsal root ganglion (DRG) neurons.

The codon for the methionine at position 129 (M129) in the human prion protein provides an alternative initiation site for translation and renders individuals homozygous for M129 more susceptible to prion disease.

Single amino-acid substitutions in the prion protein have been found to lead to resistance or susceptibility to amyloid fibril formation. In humans, the presence of methionine at position 129 in the prion protein results in increased susceptibility to prion disease, while the presence of valine at that position appears to be protective. It is hypothesized that the codon for M129 is an alternative initiation site for translation, which results in a truncated molecule that is missing the first 128 amino acids, including the signal peptide. This N-terminal truncated form of the prion molecule will not be transported to the extracellular space and thus will accumulate in the cytosol where it is more susceptible to fibril formation and aggregation; this aggregation could hinder normal degradation processes and cause disease. The results of experimental studies on truncated prion molecules support this hypothesis. To test the hypothesis, a gene segment, which when transcribed would result in a prion molecule starting at methionine 129, could be introduced into a convenient experimental animal to see if there is increased incidence of prion disease. Or, fibrils from the brains of affected M129/M129 homozygous individuals could be isolated and the molecules in the fibrils analyzed to determine the identity of the N-terminal amino acid(s). We predict that those isolates will have a preponderance of molecules that start with the methionine at position 129 in the intact protein.

Why don't humans get scrapie from eating sheep? A possible explanation based on secondary structure predictions.

In an effort to find a structural explanation for the lack of direct transmission of scrapie from sheep to humans, secondary structure predictions are used to locate the segments of the prion sequence which may be involved in the transformation from the normal form of the prion protein, which has high helix content, to the pathogenic form, which has high beta-sheet content. The Chou-Fasman algorithm, which calculates propensities for both helix and sheet formation, was used to predict the secondary structures of the scrapie-resistant and the scrapie-susceptible variants of the ovine prion protein. The scrapie-susceptible variant, which has a glutamine at residue position 168 (human prion protein numbering), is predicted to have a propensity for sheet formation in that region of the molecule, while the scrapie-resistant variant, which has an arginine at position 168, does not. The valine at position 133, additionally present in the ovine variant which is the most susceptible to scrapie, is predicted to result in even more sheet formation. When the predicted secondary structure of the human prion protein is compared to those of the ovine prion protein variants, the human protein is found to be most similar to the scrapie-resistant variant. This result is proposed to provide a possible explanation for the observation that scrapie is not directly transmitted from sheep to humans.

Are humans getting 'mad-cow disease' from eating beef, or something else?

Bovine spongiform encephalopathy (BSE) or 'mad-cow disease' is believed to have been caused by the consumption of scrapie-infected sheep matter that had been added to cattle feed. BSE is then believed to have been transmitted to humans by the consumption of infected beef. We have compared the sequences of human and various animal prion proteins with regards to the fragments that could result from gastric digestion. We noted the close similarity of the sequences of human and rodent prion proteins in a peptic fragment that corresponds very closely to one that had been shown by others to be protease resistant and infective. Since rats and mice are known to be susceptible to prion disease, we propose that ingestion of infected rodent parts, possibly droppings, may be a possible mode of transmission of scrapie or BSE to humans.

3,7-Dimethylguanine, a new purine from a Philippine sponge Zyzzya fuliginosa.

A new purine 3,7-dimethylguanine (1) has been isolated from the marine sponge Zyzzya fuliginosa, along with the known metabolites, makaluvamines A, C, K (2--4), 4-hydroxyphenylacetic acid (5), methyl ester of 4-hydroxyphenylacetic acid (6), 4-hydroxyphenethyl alcohol (7), L-phenylalanine (8) and L-tryptophan (9). The structure of 3,7-dimethylguanine (1) was elucidated by analysis of 1D and 2D (one- and two-dimensional) NMR [HMQC (heteronuclear multiple quantum coherence), gHMBC (heteronuclear multiple bond connectivity), 1H-15N gHMBC] data, mass spectroscopy data, and by comparison with 3,7-dimethylisoguanine (10).

Agelasine F from a Philippine Agelas sp. sponge exhibits in vitro antituberculosis activity.

Marine sponge samples were collected in Baler, Aurora, Philippines, and extracts were tested for in vitro antituberculosis activity. An orange Agelas sp. sponge yielded the known compound, agelasine F, which inhibited some drug resistant strains of Mycobacterium tuberculosis in vitro at concentrations as low as 3.13 micrograms/ml. Activity against M. tuberculosis residing within macrophages required concentrations of 13-22 micrograms/ml which was below the IC50 for Vero cells (34 micrograms/ml).

Makaluvamine N: a new pyrroloiminoquinone from Zyzzya fuliginosa.

Makaluvamine N (1), a new pyrroloiminoquinone, was isolated from the Philippine sponge Zyzzya fuliginosa, together with the known compounds makaluvamines A, C, D, E (2-5), and I (6). The structure of 1 was determined by spectroscopic investigation. Makaluvamine N demonstrated an ability to inhibit the catalytic activity of topoisomerase II.

Tubercidin analogs from the ascidian Didemnum voeltzkowi.

Two new 5'-deoxypyrrolo[2,3-d]pyrimidine (7-deazapurine) nucleosides, 5'-deoxytubercidin and 5'-deoxy-3-bromotubercidin, were identified from the ascidian Didemnum voeltzkowi. Two known anomers of 5'-deoxy-3-iodotubercidin were also purified from the extract. Assignments were made on the basis of 1H and 13C chemical shifts as well as HPLC-MS experiments.

Topoisomerase II-mediated DNA cleavage by adocia- and xestoquinones from the Philippine sponge Xestospongia sp.

Investigation of an orange Xestospongia sp. sponge collected at Cape Bolinao in northern Luzon, Philippines, yielded the known compounds adociaquinones A and B (1, 2) and six new metabolites, secoadociaquinones A and B (3, 4), 14-methoxyxestoquinone (5), 15-methoxyxestoquinone (6), 15-chloro-14-hydroxyxestoquinone (7), and 14-chloro-15-hydroxyxestoquinone (8). All compounds showed inhibition of topoisomerase II in catalytic DNA unwinding and/or decatenation assays. Furthermore, adociaquinone B showed activity in a KSDS assay, suggesting it inhibits the enzyme by freezing the enzyme-DNA cleavable complex. Interestingly, adociaquinone B did not displace ethidium bromide from DNA or unwind supercoiled DNA, implying it does not intercalate DNA.