The roles of homonuclear line narrowing and the H-1 amide chemical shift tensor in structure determination of proteins by solid-state NMR spectroscopy

The seminal contributions of Ulrich Haeberlen to homonuclear line narrowing and the determination of H-1 chemical shift tensors are crucial for protei n structure determination by solid-state nuclear magnetic resonance spectro scopy. The 1H chemical shift is particularly important in spectra obtained on oriented samples of membrane proteins as a mechanism for providing dispe rsion among resonances that are not resolved with the H-1-N-15 dipolar coup ling and N-15 chemical shift frequencies. This is demonstrated with three-d imensional experiments on uniformly N-15-labeled samples of Magainin antibi otic peptide and the protein Vpu from HIV-1 in oriented lipid bilayers. The se experiments enable resonances in two-dimensional H-1-N-15 dipolar coupli ng/N-15 chemical shift planes separated by H-1 chemical shift frequencies t o be resolved and analyzed. These three-dimensional spectra are compared to one-dimensional spectra of full-length Vpu, the cytoplasmic domain of Vpu, and Magainin, as well as to two-dimensional spectra of fd coat protein and Colicin El polypeptide. The H-1 amide chemical shift tensor provides valua ble structural information, and this is demonstrated with its contributions to orientational restrictions to one of the in-plane helical residues of M againin.