Structural Preferences of Neuroprotective S14G-Humanin Peptide Analyzed by Molecular Modeling and Circular Dichroism

S14G-humanin (S14G-HN) is one of the latest of a new family of neuropeptides with protective action against Alzheimer's disease insults. The structure of S14G-HN was studied with both spectroscopic techniques and molecular dynamics simulation. Secondary structure predictions and modeling of backbone conformation were carried out. Side chain reconstruction, homology modeling and molecular dynamics (MD) simulations were performed on four different models. A beta strand tendency in residues 5 to 10 and a propensity to adopt turn or irregular conformation in residues 13 to 17 was found. Circular dichroism experimental studies of S14G-HN in aquaeous solution and in different 2,2,2- trifluoroethanol (TFE) concentrations were also performed. In the absence of TFE and at low TFE concentrations, CD spectra are indicative of a small degree of ordering in the peptide. On further increment of TFE concentration, changes occur that indicate the formation of a structured conformation. Both experimental and computational results indicate that S14G-HN has a reduced helical propensity, in contrast with wild type humanin, as well as a higher conformational flexibility.