title: Folding and unfolding of helix-turn-helix motifs in the gas phase.
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.
authors.affiliation: Department of Chemistry, Indiana University, Bloomington, Indiana 47405-7102, USA.
authors.forename: Lloyd W
authors.initials: LW
authors.lastname: Zilch
authors.forename: David T
authors.initials: DT
authors.lastname: Kaleta
authors.forename: Motoya
authors.initials: M
authors.lastname: Kohtani
authors.forename: Ranjani
authors.initials: R
authors.lastname: Krishnan
authors.forename: Martin F
authors.initials: MF
authors.lastname: Jarrold
mesh_terms: D020816:Amino Acid Motifs; D003198:Computer Simulation; D005740:Gases / Q000737:chemistry; D008956:Models, Chemical; D008958:Models, Molecular; D044367:Phase Transition; D011489:Protein Denaturation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry* / Q000648:ultrastructure*; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*
chemical_list: D005740:Gases; D011506:Proteins