β-Peptides made from L-aspartic acid monomers form a new class of β3-peptides. Here we report the first three-dimensional NMR solution structure of a β3-hexapeptide (1) from L-aspartic acid monomers in 2,2,2-trifluoroethanol (TFE). We show that 1 forms a right-handed 14-helical structure in TFE. α-peptides from naturally occurring L-amino acids adopt a right-handed α-helix whereas β3-peptides formed from β3-amino acids derived from naturally occurring L-amino acids form left-handed 14-helices. The right-handed 14-helical conformation of 1 is a better mimic of α-peptide conformations. Using the NMR structure of 1 in TFE, we further study the conformation of 1 in water, as well as two similar β3-peptides (2 and 3) in water and TFE by molecular dynamics (MD) simulations. NMR and MD results suggest loss of secondary structure of 1 in water and show that it forms a fully extended structure. 2 and 3 contain residues with oppositely charged side chains that engage in salt-bridge interactions and dramatically stabilize the 14-helical conformation in aqueous media.
Kaur K, Sprules T, Soliman W, Beleid R, Ahmed S. Right-handed 14-helix in beta(3)-peptides from l-aspartic acid monomers. Biochim. Biophys. Acta. 2008;1784(4):658-665. doi: 10.1016/j.bbapap.2008.01.009
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