NMR Determination of the Torsion Angle Ψ in α-Helical Peptides and Proteins: The HCCN Dipolar Correlation Experiment

✍ Scribed by Vladimir Ladizhansky; Mikhail Veshtort; Robert G. Griffin

• Publisher: Elsevier Science
• Year: 2002
• Tongue: English
• Weight: 179 KB
• Volume: 154
• Category: Article
• ISSN: 1090-7807
• DOI: 10.1006/jmre.2001.2488

✦ Synopsis

Several existing methods permit measurement of the torsion angles φ, ψ and χ in peptides and proteins with solid-state MAS NMR experiments. Currently, however, there is not an approach that is applicable to measurement of ψ in the angular range -20 • to -70 • , commonly found in α-helical structures. Accordingly, we have developed a HCCN dipolar correlation MAS experiment that is sensitive and accurate in this regime. An initial REDOR driven 13 C -15 N dipolar evolution period is followed by the C to C α polarization transfer and by Lee-Goldburg cross polarization recoupling of the 13 C α 1 H dipolar interaction. The difference between the effective 13 C 1 H and 13 C 15 N dipolar interaction strengths is balanced out by incrementing the 13 C-15 N dipolar evolution period in steps that are a factor of R(R ∼ ω CH /ω CN ) larger than the 13 C-1 H steps. The resulting dephasing curves are sensitive to variations in ψ in the angular region associated with α-helical secondary structure. To demonstrate the validity of the technique, we apply it to N-formyl-[U-13 C, 15 N] Met-Leu-Phe-OH (MLF). The value of ψ extracted is consistent with the previous NMR measurements and close to that reported in diffraction studies for the methyl ester of MLF, N-formyl-[U-13 C, 15 N]Met-Leu-Phe-OMe.