title: Comparison of 15N- and 13C-determined parameters of mobility in melittin.
abstract: Backbone and tryptophan side-chain mobilities in the 26-residue, cytolytic peptide melittin (MLT) were investigated by 15N and 13C NMR. Specifically, inverse-detected 15N T1 and steady-state NOE measurements were made at 30 and 51 MHz on MLT at 22 degrees C enriched with 15N at six amide positions and in the Trp19 side chain. Both the disordered MLT monomer (1.2 mM peptide at pH 3.6 in neat water) and alpha-helical MLT tetramer (4.0 mM peptide at pH 5.2 in 150 mM phosphate buffer) were examined. The relaxation data were analyzed in terms of the Lipari and Szabo model-free formalism with three parameters: tau m, the correlation time for the overall rotation; S2, a site-specific order parameter which is a measure of the amplitude of the internal motion; and tau e, a local, effective correlation time of the internal motion. A comparison was made of motional parameters from the 15N measurements and from 13C measurements on MLT, the latter having been made here and previously [Kemple et al. (1997) Biochemistry, 36, 1678-1688]. tau m and tau e values were consistent from data on the two nuclei. In the MLT monomer, S2 values for the backbone N-H and C alpha-H vectors in the same residue were similar in value but in the tetramer the N-H order parameters were about 0.2 units larger than the C alpha-H order parameters. The Trp side-chain N-H and C-H order parameters, and tau e values were generally similar in both the monomer and tetramer. Implications of these results regarding the dynamics of MLT are examined.
authors.affiliation: Department of Physics, Indiana University Purdue University, Indianapolis 46202-3273, USA.
authors.forename: L
authors.initials: L
authors.lastname: Zhu
authors.forename: F G
authors.initials: FG
authors.lastname: Prendergast
authors.forename: M D
authors.initials: MD
authors.lastname: Kemple
mesh_terms: D000595:Amino Acid Sequence; D002247:Carbon Isotopes; D007553:Isotope Labeling; D046911:Macromolecular Substances; D008555:Melitten / Q000737:chemistry*; D008969:Molecular Sequence Data; D009587:Nitrogen Isotopes; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D011487:Protein Conformation
chemical_list: D002247:Carbon Isotopes; D046911:Macromolecular Substances; D009587:Nitrogen Isotopes; D008555:Melitten