Metabarcoding Used for the First Time to Identify Prey of Wild Totoaba macdonaldi.

Totoaba macdonaldi is an endangered endemic fish of the Gulf of California. Overexploitation resulted in the Mexican government banning the fishing of this species in 1975, and it being listed as endangered. However, the species is still subject to illegal fishing. Despite its conservation status, little is known about totoaba biology. The present study aimed to implement, for the first time, a metabarcoding protocol to describe the totoaba diet. Four wild totoaba individuals, seized by Mexican law enforcement agents, were dissected, and their stomach contents were collected. Three representative amplicon libraries were generated for cephalopods, chordates, and eukaryotes. After sequencing, 18 different taxa were identified, of which 11 species were recognized as prey. The totoaba were found to have consumed Pacific anchovy (Cetengraulis mysticetus), flathead grey mullet (Mugil cephalus), bigeye croaker (Micropogonias megalops), northern anchovy (Engraulis mordax), ocean whitefish (Caulolatilus princeps), milkfish (Chanos chanos), and Pacific sardine (Sardinops sagax). Members of the Euphausiidae family (krill) were also identified. This study identified up to four times more species in much fewer samples than previous studies based on morphological recognition, thus confirming metabarcoding as an effective method for studying the feeding habits of this species and one providing the tools required for further analysis of the totoaba diet.

The N-terminal tandem repeat region of human prion protein reduces copper: role of tryptophan residues.

Prion protein (PrP) has attracted considerable attention, mainly due to its involvement in transmissible spongiform encephalopathies. Toward its N-terminal region, PrP bears an octapeptide repeat which has been shown to bind copper. We found that a human synthetic peptide (PrP(59-91)), corresponding to the four repeats of Pro-His-Gly-Gly-Gly-Trp-Gly-Gln has the ability to reduce copper. A mutant peptide lacking tryptophan displayed only 24% of the wild-type copper-reducing activity. Experiments performed in a N(2) environment confirmed that O(2) is not involved in the reaction. Our results indicated that cell surface PrP, besides its ability to bind copper, bears the capacity to reduce copper in vitro. The potential physiological role of copper reduction by PrP is discussed.

Amyloid-beta-peptide reduces copper(II) to copper(I) independent of its aggregation state.

Alzheimer's disease (AD) is characterized by the deposition of amyloid beta-peptide (A beta) and neuronal degeneration in brain regions involved in learning and memory. One of the leading etiologic hypotheses regarding AD is the involvement of free radical-mediated oxidative stress in neuronal degeneration. Recent evidence suggests that metals concentrated in amyloid deposits may contribute to the oxidative insults observed in AD-affected brains. We hypothesized that A beta peptide in the presence of copper enhances its neurotoxicity generating free radicals via copper reduction. In the present study, we have examined the effect of the aggregation state of amyloid-beta-peptide on copper reduction. In independent experiments we measured the copper-reducing ability of soluble and fibrillar A beta(1-40) forms by bathocuproine assays. As it was previously observed for the amyloid precursor protein (APP), the A beta peptide showed copper-reducing ability. The capacity of A beta to reduce copper was independent of the aggregation state. Finally, the A beta peptide derived from the human sequence has a greater effect than the A beta peptide derived from the rat sequence, suggesting that histidine 13 may play a role in copper reduction. In agreement with this possibility, the A beta peptide reduces less copper in the presence of exogenous histidine.

Amyloid-beta-peptide reduces copper(II) to copper(I) independent of its aggregation state

Alzheimer's disease (AD) is characterized by the deposition of amyloid beta-peptide (A beta) and neuronal degeneration in brain regions involved in learning and memory. One of the leading etiologic hypotheses regarding AD is the involvement of free radical-mediated oxidative stress in neuronal degeneration. Recent evidence suggests that metals concentrated in amyloid deposits may contribute to the oxidative insults observed in AD-affected brains. We hypothesized that A beta peptide in the presence of copper enhances its neurotoxicity generating free radicals via copper reduction. In the present study, we have examined the effect of the aggregation state of amyloid-beta-peptide on copper reduction. In independent experiments we measured the copper-reducing ability of soluble and fibrillar A beta(1-40) forms by bathocuproine assays. As it was previously observed for the amyloid precursor protein (APP), the A beta peptide showed copper-reducing ability. The capacity of A beta to reduce copper was independent of the aggregation state. Finally, the A beta peptide derived from the human sequence has a greater effect than the A beta peptide derived from the rat sequence, suggesting that histidine 13 may play a role in copper reduction. In agreement with this possibility, the A beta peptide reduces less copper in the presence of exogenous histidine.

Cysteine 144 is a key residue in the copper reduction by the beta-amyloid precursor protein.

The beta-amyloid precursor protein (beta-APP) contains a copper-binding site localized between amino acids 135 and 156 (beta-APP(135-156)). We have employed synthetic beta-APP peptides to characterize their capacities to reduce Cu(II) to Cu(I). Analogues of the wild-type beta-APP(135-156) peptide, containing specific amino acid substitutions, were used to establish which residues are specifically involved in the reduction of copper by beta-APP(135-156). We report here that beta-APP's copper-binding domain reduced Cu(II) to Cu(I). The single-mutant beta-APP(His147-->Ala) and the double-mutant beta-APP(His147-->Ala/His149-->Ala) showed a small decrease in copper reduction in relation to the wild-type peptide and the beta-APP(Cys144-->Ser) mutation abolished it, suggesting that Cys144 is the key amino acid in the oxidoreduction reaction. Our results confirm that soluble beta-APP is involved in the reduction of Cu(II) to Cu(I).