Determination of Polypeptide Backbone Dihedral Angles in Solid State NMR by Double Quantum 13C Chemical Shift Anisotropy Measurements

✍ Scribed by Francisco J. Blanco; Robert Tycko

• Publisher: Elsevier Science
• Year: 2001
• Tongue: English
• Weight: 238 KB
• Volume: 149
• Category: Article
• ISSN: 1090-7807
• DOI: 10.1006/jmre.2000.2281

✦ Synopsis

A solid state NMR technique for the determination of peptide backbone conformations at specific sites in unoriented samples under magic angle spinning (MAS) is described and demonstrated on a doubly labeled polycrystalline sample of the tripeptide AlaGlyGly and a sextuply labeled lyophilized sample of the 17-residue peptide MB(i + 4)EK. The technique is applicable to peptides and proteins that are labeled with 13 C at two (or more) consecutive backbone carbonyl sites. Double quantum (DQ) coherences are excited with a radiofrequency-driven recoupling sequence and evolve during a constant-time t 1 period at the sum of the two anisotropic chemical shifts. The relative orientation of the two chemical shift anisotropy (CSA) tensors, which depends on the φ and ψ backbone dihedral angles, determines the t 1 -dependence of spinning sideband intensities in the DQ-filtered 13 C MAS spectrum. Experiments and simulations show that both dihedral angles can be extracted from a single data set. This technique, called DQCSA spectroscopy, may be especially useful when analyzing the backbone conformation of a polypeptide at a particular doubly labeled site in the presence of additional labeled carbons along the sequence.