Short and long range 2D 15Nâ??15N NMR correlations among peptide groups by novel solid state dipolar mixing schemes
 

Short and long range 2D 15Nâ??15N NMR correlations among peptide groups by novel solid state dipolar mixing schemes

Abstract

A recently developed homonuclear dipolar recoupling scheme, Adiabatic Linearly FREquency Swept reCOupling (AL FRESCO), was applied to record two-dimensional (2D) 15Nâ??15N correlations on uniformly 15N-labeled GB1 powders. A major feature exploited in these 15Nâ??15N correlations was AL FRESCOâ??s remarkably low RF power demands, which enabled seconds-long mixing schemes when establishing direct correlations. These 15Nâ??15N mixing schemes proved efficient regardless of the magic-angle spinning (MAS) rate and, being nearly free from dipolar truncation effects, they enabled the detection of long-range, weak dipolar couplings, even in the presence of strong short-range dipolar couplings. This led to a connectivity information that was significantly better than that obtained with spontaneously proton-driven, 15N spin-diffusion experiments. An indirect approach producing long-range 15Nâ??15N correlations was also tested, relying on short (ms-long) 1HNâ??1HN mixings schemes while applying AL FRESCO chirped pulses along the 15N channel. These indirect mixing schemes produced numerous long-distance Niâ??Ni±n (nâ??=â??2â??â??â??5) correlations, that might be useful for characterizing three-dimensional arrangements in proteins. Once again, these AL FRESCO mediated experiments proved more informative than variants based on spin-diffusion-based 1HNâ??1HN counterparts.



Source: Journal of Biomolecular NMR