NMR evidence for multiple conformations in a highly helical model peptide.
A monomeric model peptide, acetyl-WEAQAREALAKEAAARA-amide, has been structurally characterized using the complementary techniques of 1H 2D NMR and circular dichroism. Temperature-dependent CD measurements are consistent with a two-state helix/coil transition model and indicate a 65% contribution of helical conformers at 5 degrees C. Homonuclear 2D NMR experiments allowed the assignment of all proton resonances. The analysis of NOE-type cross-relaxation data established a large number of specific short- and medium-range NOE connectivities throughout the peptide, confirming the highly helical character of the peptide. However, the observation of long-range NOEs between the methyl protons of leucine-9 and backbone and side-chain protons of amino acids located at the N-terminus, as well as other unusual NOEs, unambiguously reflects the existence of significantly populated nonhelical structured conformers, indicating a multiconformational equilibrium. Implications of these observations with regard to secondary structure quantitation and current method limitations are discussed.
Merutka
G
G
Department of Molecular Biology, Scripps Research Institute, La Jolla, California 92037.
Morikis
D
D
Brüschweiler
R
R
Wright
P E
PE
D000595:Amino Acid Sequence; D002942:Circular Dichroism; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry*; D017433:Protein Structure, Secondary; D013329:Structure-Activity Relationship
D010455:Peptides