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Updated: Jul 14, 2026

Single-molecule Manipulation of G-quadruplexes by Magnetic Tweezers
Published on: September 19, 2017
Folding and unfolding of helix-turn-helix motifs in the gas phase
Lloyd W Zilch1, David T Kaleta, Motoya Kohtani
1Department of Chemistry, Indiana University, Bloomington, Indiana 47405-7102, USA.
Abstract:
Ion mobility measurements and molecular dynamic simulations have been performed for a series of peptides designed to have helix-turn-helix motifs. For peptides with two helical sections linked by a short loop region: AcA(14)KG(3)A(14)K+2H(+), AcA(14)KG(5)A(14)K+2H(+), AcA(14)KG(7)A(14)K+2H(+), and AcA(14)KSar(3)A(14)K+2H(+) (Ac = acetyl, A = alanine, G = glycine, Sar = sarcosine and K = lysine); a coiled-coil geometry with two anti-parallel helices is the lowest energy conformation. The helices uncouple and the coiled-coil unfolds as the temperature is raised. Equilibrium constants determined as a function of temperature yield enthalpy and entropy changes for the unfolding of the coiled-coil. The enthalpy and entropy changes depend on the length and nature of the loop region. For a peptide with three helical sections: protonated AcA(14)KG(3)A(14)KG(3)A(14)K; a coiled-coil bundle with three helices side-by-side is substantially less stable than a geometry with two helices in an antiparallel coiled-coil and the third helix collinear with one of the other two.
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