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Investigation of finite‐pulse radiofrequency‐driven recoupling methods for measurement of intercarbonyl distances in polycrystalline and membrane‐associated HIV fusion peptide samples
Author(s) -
Zheng Zhaoxiong,
Qiang Wei,
Weliky David P.
Publication year - 2007
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.2160
Subject(s) - chemistry , membrane , peptide , fusion , crystallite , nuclear magnetic resonance , pulse (music) , lipid bilayer fusion , crystallography , optics , biochemistry , physics , detector , philosophy , linguistics
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. Copyright © 2007 John Wiley & Sons, Ltd.