Investigation of finite-pulse radiofrequency-driven recoupling methods for measurement of intercarbonyl distances in polycrystalline and membrane-associated HIV fusion peptide samples.
Two finite-pulse radiofrequency-driven recoupling (RFDR) methods were compared and applied to the measurement of 3-6 Å (13)CO-(13)CO distances in polycrystalline and membrane-associated HIV fusion peptide (HFP) samples. The RFDR methods were based on π pulses and were relatively straightforward to implement and insensitive to pulse imperfections. The two tested methods were: (i) constant-time double-quantum buildup with finite pulses (fpCTDQBU) for which the pulse sequence maintained a constant transverse relaxation period while allowing a variable period of dipolar dephasing; and (ii) constant-time finite-pulse rf-driven recoupling (fpRFDR-CT) for which the duration of transverse relaxation increased with increasing dephasing period. The fpRFDR-CT method yielded higher signal-to-noise and an accurate determination of a ~5 Å intercarbonyl distance was made in a crystalline peptide which had T(2) ≈ 55 ms. In some contrast, the HFP samples had T(2) ≈ 15 ms and the fpRFDR-CT data were dominated by transverse relaxation. Examination of the fpCTDQBU sequence showed: (i) the most rapid signal buildup was obtained with application of one (13) C π pulse per rotor period rather than one (13)C π pulse per multiple rotor periods and (ii) the data were insensitive to ~15 ppm transmitter offset and to ~5° variation of π pulse nutation angle. For HFP samples which were (13)CO labeled at a single residue, analyses of the fpCTDQBU data were interpreted with a model of mixed parallel and antiparallel β-strand arrangements in the N-terminal region of HFP and loss of parallel β-sheet structure in the C-terminal region of HFP.
D000595:Amino Acid Sequence; D003460:Crystallization; D006678:HIV / Q000737:chemistry*; D007930:Leucine / Q000031:analogs & derivatives / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008561:Membrane Fusion; D008563:Membrane Lipids / Q000737:chemistry*; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D011846:Radio Waves; D059629:Signal-To-Noise Ratio; D014760:Viral Fusion Proteins / Q000737:chemistry*
D008563:Membrane Lipids; D014760:Viral Fusion Proteins; D007930:Leucine; C088117:acetylleucine