Optimal-Control-Based Cß Chemical Shift Encoding for Efficient Signal Assignment of Solid Proteins.

ABSTRACT

Fast magic-angle spinning (MAS) solid-state NMR spectroscopy is a powerful tool for gaining structural and dynamic information on solid proteins. To access such information site-specifically, the signal assignment process is unavoidable. In the assignment process, Cα and Cß chemical shifts are of paramount importance in identifying the type of amino acid residues. Conventionally, however, recording the Cß chemical shift of solid proteins with relatively short transverse relaxation time is often limited by the long delay required for the magnetization transfer to Cß spins and its evolution, that is, by the sensitivity drop. In this article, we propose a new method that encodes the Cß chemical shifts onto the intensities of the scalar-coupled Cα signals by combining an optimal control-based spin manipulation pulse and a spin-state filter. This reduces the total required transverse evolution to less than half of that for the previously proposed method, opening up the concept of the Cß-encoding nearest-neighbor NMR, for the first time, to solid proteins. Also, the total measurement time was shorter than that required for the explicit Cß shift evolution. We demonstrate the sequential signal assignment for microcrystalline protein GB1, and then discuss the prospects for more challenging proteins.