2D NMR analysis of the conformational and dynamic properties of alpha-helical poly-gamma-benzyl L-glutamate.

Two dimensional nuclear Overhauser experiments (2D NOE) have been used to study the conformational and dynamic properties of a 20 amino acid alpha-helix of poly-gamma-benzyl L-glutamate (PBLG). The diagonal and cross peak volumes have been measured for ten different mixing times and have been used to determine the selective spin-lattice relaxation times and the cross relaxation rates between those protons which are in close proximity. Together with the nonselective relaxation rates, these values can be used to determine the effective correlation times. The results show that the correlation times for the NH and alphaH are equal and the same as expected for a rigid 20 amino acid helix, while betaH and gammaH show internal motion relative to the overall tumbling. Following determination of the effective correlation time, the proton-proton distances can be calculated from the cross relaxation rates obtained from the initial build up of the cross peak volumes. The proton-proton distances determined by this approach fall within the range expected for an alpha- helix and provide sufficient information to define the conformation.