Background:
Amyloid fibrils in Alzheimer’s disease are composed of amyloid-β (Aβ)
peptides of variant lengths. Humanin (HN), a 24 amino acid residue neuroprotective peptide, is
known to interact with the predominant Aβ isoform in the brain, Aβ (1-40).
Methods:
Here, we constructed smaller segments of Aβ and HN and identified residues in HN important
for both HN-HN and HN-Aβ interactions. Peptides corresponding to amino acid residues 5-
15 of HN, HN (5-15), HN (5-15, L11S), where Leu11 was replaced with Ser, and residues 17-28 of
Aβ, Aβ (17-28), were synthesized and tested for their ability to block formation of the complex
between HN and Aβ (1-40).
Results:
Co-immunoprecipitation and binding kinetics showed that HN (5-15) was more efficient at
blocking the complex between HN and Aβ (1-40) than either HN (5-15, L11S) or Aβ (17-28). Binding
kinetics of these smaller peptides with either full-length HN or Aβ (1-40) showed that HN (5-
15) was able to bind either Aβ (1-40) or HN more efficiently than HN (5-15, L11S) or Aβ (17-28).
Compared to full-length HN, however, HN (5-15) bound Aβ (1-40) with a weaker affinity suggesting
that while HN (5-15) binds Aβ, other residues in the full length HN peptide are necessary for
maximum interactions.
Conclusion:
L11 was more important for interactions with Aβ (1-40) than with HN. Aβ (17-28)
was relatively ineffective at binding to either Aβ (1-40) or HN. Moreover, HN, and the smaller HN
(5-15), HN (5-15 L11S), and Aβ (17-28) peptides, had different effects on regulating Aβ (1-40)
aggregation kinetics.
Orange peels, soybean hulls, Ilex paraguariensis and Platanus x hispanica were evaluated as solid substrates in order to produce peptidases from Aspergillus niger NRRL3 (PAN) under solid-state fermentation. The mixture of soybean hulls and orange peels enabled fungal development and showed the highest peptidase production. The optimal conditions for PAN production were found to be as follows: soybean hulls/orange peels mass ratio, 0.25; initial pH, 7.05; K 2 HPO 4 43.5 g/L and 4.03 g/L NaNO ; inoculation with 5000 conidia per 3g of solid substrate; incubation conditions, 30°C for 5 days. Under these conditions, the peptidase activity was 1000 ± 100 AU/mL. PAN concentration was performed by adsorption on a DEAE-cellulose matrix. The subsequent purification was carried out by gel filtration on Sephadex G-100, with a global purification factor of about 9. PAN proved to belong to the serinetype of peptidases, its highest peptidase activity being at 65 °C. However, proteolysis at 60 °C proved more suitable due to the differences in the inactivation rate. Besides, PAN showed high stability over a pH range of 4 to 11. Taking all this into account, we herein describe the production and purification of a serine peptidase from Aspergillus niger NRRL3 for the first time.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.