Magic Angle Spinning NMR Structure Determination of Proteins from Pseudocontact Shifts

Magic angle spinning solid-state NMR is a unique technique to study atomic-resolution structure of biomacromoleles which resist crystallization or are too large to study by solution NMR techniques. However, difficulties in obtaining sufficient number of long-range distance restraints using dipolar coupling based spectra hamper the process of structure determination of proteins in solid-state NMR. In this study it is sown that high-resolution structure of proteins in solid phase can e determined without the use of traditional dipolar-dipolar coupling based distance restraints by combining the measurements of pseudocontact shifts (PCSs) with Rosetta calculations. The PCSs were generated by chelating exogenous paramagnetic metal ions to a tag 4-mercaptomcthyl-dipicolinic acid, which is covalently attached to different residue sites in a 56-residue immunogobulin-binding domain of protein G(GB1). The long-range structural restraints with metal-nucleus distance of up similar to 20 angstrom are quantitatively extracted from experimentally observed PCSs, and these are in good agreement with the distances back-calculated using an X-ray structure model. Moreover, we demonstrate that using several paramagnetic ions with varied paramagnetic suspectibilities as well as the introduction of paramagnetic labels at different sites can dramatically increase the number of long-range restraints and cover different regions of the protein. The structure generated from solid-state NMR PCSs restraints combined with Rosetta calculations has 0.7 angstrom root-mean-square deviation relative to X-ray structure.