A Study of the Influence of Charged Residues on β-Hairpin Formation by Nuclear Magnetic Resonance and Molecular Dynamics

Chain reversals are often nucleation sites in protein folding. The β-hairpins of FBP28 WW domain and IgG are stable and have been proved to initiate the folding and are, therefore, suitable for studying the influence of charged residues on β-hairpin conformation. In this paper, we carried out NMR examination of the conformations in solution of two fragments from the FPB28 protein (PDB code: 1E0L) (N-terminal part) namely KTADGKT-NH(2) (1E0L 12–18, D7) and YKTADGKTY-NH(2) (1E0L 11–19, D9), one from the B3 domain of the protein G (PDB code: 1IGD), namely DDATKT-NH(2) (1IGD 51–56) (Dag1), and three variants of Dag1 peptide: DVATKT-NH(2) (Dag2), OVATKT-NH(2) (Dag3) and KVATKT-NH(2) (Dag4), respectively, in which the original charged residue were replaced with non-polar residues or modified charged residues. It was found that both the D7 and D9 peptides form a large fraction bent conformations. However, no hydrophobic contacts between the terminal Tyr residues of D9 occur, which suggests that the presence of a pair of like-charged residues stabilizes chain reversal. Conversely, only the Dag1 and Dag2 peptides exhibit some chain reversal; replacing the second aspartic-acid residue with a valine and the first one with a basic residue results in a nearly extended conformation. These results suggest that basic residues farther away in sequence can result in stabilization of chain reversal owing to screening of the non-polar core. Conversely, smaller distance in sequence prohibits this screening, while the presence oppositely-charged residues can stabilize a turn because of salt-bridge formation. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s10930-014-9585-7) contains supplementary material, which is available to authorized users.