Rationally designed turn promoting mutation in the amyloid β-peptide sequence to stabilize oligomers in solution.

P. Novick, J. Rajadas, C.W. Liu, N. W. Kelley, M. Inayathullah, and V. S. Pande.

PLoS ONE (2011)

It is believed that Alzheimer’s Disease results from the misfolding of the Abeta peptide. Understanding how Abeta misfolds could give us some key insights into how to cure Alzheimer’s Disease. This paper experimentally tests a key prediction made in an earlier paper (paper #58: “Simulating oligomerization at experimental concentrations and long timescales: A Markov state model approach” by Nicholas W. Kelley, V. Vishal, Grant A. Krafft, and Vijay S. Pande. J. Chem. Phys. 129, 214707 (2008); DOI:10.1063/1.3010881). In this paper, we show experimentally that there appears to be a beta turn in the Abeta as predicted. This leads to a very stable form of misfolded Abeta which could be used as a starting point for a new Alzheimer’s therapy. We are heavily pursuing this research direction at the moment.

Enhanced production of a 42-residue beta amyloid peptide (Aβ42) in affected parts of the brain has been suggested to be the main causative factor for the development of Alzheimer’s Disease (AD). The severity of the disease depends not only on the amount of the peptide but also its conformational transition leading to the formation of oligomeric amyloid-derived diffusible ligands (ADDLs) in the brain of AD patients. Despite being significant to the understanding of AD mechanism, no atomic-resolution structures are available for these species due to the evanescent nature of ADDLs that hinders most structural biophysical investigations. Based on our molecular modeling and computational studies, we have designed Met35Nle and G37p mutations in the Aβ42 peptide (Aβ42Nle35p37) that appear to organize Aβ42 into stable oligomers. 2D NMR on the Aβ42Nle35p37 peptide revealed the occurrence of two β-turns in the V24-N27 and V36-V39 stretches that could be the possible cause for the oligomer stability. We did not observe corresponding NOEs for the V24-N27 turn in the Aβ21–43Nle35p37 fragment suggesting the need for the longer length amyloid peptide to form the stable oligomer promoting conformation. Because of the presence of two turns in the mutant peptide which were absent in solid state NMR structures for the fibrils, we propose, fibril formation might be hindered. The biophysical information obtained in this work could aid in the development of structural models for toxic oligomer formation that could facilitate the development of therapeutic approaches to AD.