title: Solution structure of a bent alpha-helix.
abstract: We present the solution structure determination of a peptide with sequence Ac-WEAQAREALAKEAQARA-NH2, using NMR data. The peptide has a high population of a stable alpha-helical structure in the middle with fraying ends. In addition, our data are consistent with the presence of several other transient and interconverting conformers. The peptide sequence was designed using amino acids that have propensity for alpha-helix specificity. The presence of E-R/K (i, i + 4) ion pairs was expected to enhance the stability of the alpha-helix by introducing favorable electrostatic interactions at the side chain level, in addition to the characteristic backbone (i, i + 4) hydrogen bonds. The NMR structural ensemble demonstrates competition between E-R/K (i, i + 4) and (i, i - 1) ion pair formation, with the (i, i - 1) interactions being dominant. The relative topologies of the charged side chains demonstrate flexibility and overall compromised favorable medium/long-range electrostatic interactions. The peptide alpha-helix is bent despite the lack of an amphipathic sequence. Bending is introduced by a strong (i, i + 8) hydrophobic interaction between the side chains of N-terminal tryptophan and leucine at the middle of the peptide sequence.
authors.affiliation: Department of Chemistry, University of California, Riverside, California 92521, USA.
authors.forename: Li
authors.initials: L
authors.lastname: Zhang
authors.forename: Dimitrios
authors.initials: D
authors.lastname: Morikis
mesh_terms: D004578:Electron Spin Resonance Spectroscopy; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D010455:Peptides / Q000737:chemistry*; D017433:Protein Structure, Secondary
chemical_list: D010455:Peptides; C525145:acetyl-tryptophyl-glutamyl-alanyl-glutaminyl-alanyl-arginyl-glutamyl-alanyl-leucyl-alanyl-lysyl-glutamyl-alanyl-glutaminyl-alanyl-arginyl-alaninamide