title: Energetic characterization of short helical polyalanine peptides in water: analysis of 13C=O chemical shift data.
abstract: Measured at 2 degrees C in water, NMR chemical shifts of (13)C=O labeled central alanine residues of peptides W-Lys(5)-(t)L(3)-Ala(n)-(t)L(3)-Lys(5)NH(2), n = 9, 11, 13, 15, 19 and W-Lys(5)-(t)L(3)-a-Ala(n)-A-Inp-(t)L(2)-Lys(5)NH(2) (a = D-Ala; (t)L = tert-leucine; Inp = 4-carboxypiperidine) are used to assign jt(L) and ct(L), the N- and C-terminal (t)L capping parameters and length-dependent values for w(Ala)(n), the alanine helical propensity for Ala(n) peptides. These parameters allow Lifson-Roig characterization of the stabilities of Ala(n)() helices in water. To facilitate chemical shift characterization, different (13)C/(12)C ratios are incorporated into specific Ala sites to code up to six residue sites per peptide. Large left/right chemical shift anisotropies are intrinsic to helical polyalanines, and a correcting L-R-based model is introduced. Capping parameters jt(L) = ct(L) lie in the range of 0.3 to 0.5; the (t)L residues are thus moderately helix-destabilizing. For helical conformations of lengths shorter than eight residues, assigned values for w(Ala) approach 1.0 but increase monotonically with length to a value of 1.59 for w(Ala)(19).
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, Cambridge, 02139, USA.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Kennedy
authors.forename: Sharon M
authors.initials: SM
authors.lastname: Walker
authors.forename: Daniel S
authors.initials: DS
authors.lastname: Kemp
mesh_terms: D000409:Alanine / Q000737:chemistry; D002247:Carbon Isotopes; D002942:Circular Dichroism; D008956:Models, Chemical; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D010455:Peptides / Q000737:chemistry*; D017433:Protein Structure, Secondary; D014867:Water / Q000737:chemistry
chemical_list: D002247:Carbon Isotopes; D010455:Peptides; D014867:Water; C019529:polyalanine; D000409:Alanine