Elucidation of the Aggregation Pathways of Helix–Turn–Helix Peptides: Stabilization at the Turn Region Is Critical for Fibril Formation Thanh D. Do Ali Chamas Xueyun Zheng Aaron Barnes Dayna Chang Tjitske Veldstra Harmeet Takhar Nicolette Dressler Benjamin Trapp Kylie Miller Audrene McMahon Stephen C. Meredith Joan-Emma Shea Kristi Lazar Cantrell Michael T. Bowers 10.1021/acs.biochem.5b00414.s001 https://acs.figshare.com/articles/dataset/Elucidation_of_the_Aggregation_Pathways_of_Helix_Turn_Helix_Peptides_Stabilization_at_the_Turn_Region_Is_Critical_for_Fibril_Formation/2152117 Aggregation of proteins to fiberlike aggregates often involves a transformation of native monomers to β-sheet-rich oligomers. This general observation underestimates the importance of α-helical segments in the aggregation cascade. Here, using a combination of experimental techniques and accelerated molecular dynamics simulations, we investigate the aggregation of a 43-residue, apolipoprotein A-I mimetic peptide and its E21Q and D26N mutants. Our study indicates a strong propensity of helical segments not to adopt cross-β-fibrils. The helix–turn–helix monomeric conformation of the peptides is preserved in the mature fibrils. Furthermore, we reveal opposite effects of mutations on and near the turn region in the self-assembly of these peptides. We show that the E21–R24 salt bridge is a major contributor to helix–turn–helix folding, subsequently leading to abundant fibril formation. On the other hand, the K19–D26 interaction is not required to fold the native helix–turn–helix peptide. However, removal of the charged D26 residue decreases the stability of the helix–turn–helix monomer and consequently reduces the level of aggregation. Finally, we provide a more refined assembly model for the helix–turn–helix peptides from apolipoprotein A-I based on the parallel stacking of helix–turn–helix dimers. 2015-07-07 00:00:00 aggregation cascade fiberlike aggregates helix peptide helical segments fibril formation Aggregation Pathways Fibril FormationAggregation assembly model D 26N mutants D 26 residue decreases E 21Q dynamics simulations