Lactam Bridge Stabilization of α-Helices:  The Role of Hydrophobicity in Controlling Dimeric versus Monomeric α-Helices

Abstract

A series of lactam-bridged and linear 14 residue amphipathic alpha-helical peptides based on the sequence Ac-EXEALKKEXEALKK-amide were prepared in order to determine the effect of decreasing the hydrophobicity of the nonpolar face to helical content and stability. This was done by substituting position X by Ile, Val, and Ala. Lactam bridges spaced i to i + 4 were formed between the side chains of Glu3 and Lys7 and Glu10 and Lys14 while the linear noncyclized peptides could potentially form i to i + 4 salt bridges with the same residues. It was found that in all cases the lactam-bridged peptides were substantially more helical than the corresponding linear peptides as determined by CD spectroscopy. Moreover, the helical content approached 100% for the lactam-bridged peptides X = Ile and Ala and was greater than 80% for X = Val. For X = Ile and Val, this was partly due to the ability of the lactam bridges to enhance interchain interactions relative to the linear versions of the same sequence. Size-exclusion chromatography demonstrated that the Ile-based peptide associates as a dimer. The alanine-based lactam-bridged peptide was found to be monomeric as determined by concentration dependency studies and size-exclusion chromatography. Thermal denaturation studies in benign media indicated that the lactam-based peptides were very stable. The conformation of the Ala-based lactam peptide was further characterized by two-dimensional NMR spectroscopy and was found to be highly helical. The results demonstrate the ability of lactam bridges to stabilize the helical conformation and enhance dimerization of peptides based on a 3,4 hydrophobic heptad repeat. The substitution of Ala residues in the hydrophobic face of the alpha-helix can prevent dimerization and specify monomeric helical structure.

Binding of an Oligopeptide to a Specific Plane of Ice

“…Previously it has been shown that incorporation of a lactam bridge between Glu and Lys spaced four residues apart dramatically increased the helical content of small amphipathic peptides relative to their uncyclized linear peptides bearing the same sequence (13). The modified peptide 15EK was ideally suited for lactam bridge synthesis because of the orientation of the ion pair, Glu-7 and Lys-11.…”

“…Peptide Synthesis, Purification, and Mass Analysis-All peptides were prepared by solid-phase peptide synthesis using a benzhydrylamine hydrochloride resin on a Labortec SP 640 peptide synthesizer as described previously (13). The peptides were cleaved from the resin by reaction with HF (10 ml/g resin) containing 10% anisole for 1 h at Ϫ5°C to 0°C.…”

Folding of the C-Terminal Fragment V111-D143 of Staphylococcal Nuclease in Aqueous Solution

“…In the sequence region E122-K136, E129 and K133 are the two residues located on the same face of the corresponding helix 3 in native SNase. As was indicated, the side-chain-to-side-chain lactam bridges of (i, i+4) spaced residues glutamic-lysine can induce or stabilize helical structure in peptides [27,28]. This implies that the possible interactions between side chains of E129 and K133 in SNase(111-143) could induce the helical structure in the corresponding segment.…”

Synthesis and NMR solution structure of an α‐helical hairpin stapled with two disulfide bridges

“…and inhibit fraying of the N-and C-termini, which in turn enhance hydrophobic interactions required for coiled-coil stabilization. Nevertheless, it has been demonstrated that the introduction of a disulfide crosslink between the two helices, via an appropriate linker, is often necessary to further stabilize newly designed coiled-coil structures Houston et al, 1996a!. In the case of a 2 p8, the stabilization of the coiled-coil conformation is obtained with a thermodynamically favorable canonical geometry both for the disulfides and the helices, as well as through proper packing of the hydrophobic side chains at the helix interface.…”