Deoxyribose ring conformation of [d(GGTATACC)]2: an analysis of vicinal proton-proton coupling constants from two-dimensional proton nuclear magnetic resonance

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Abstract
Exchangeable and nonexchangeable protons of [d(GGTATACC)]2 in aqueous cacodylate solution were assigned from two-dimensional nuclear Overhausser effect (2D NOE) spectra. With phase-sensitive COSY and double quantum filtered COSY (DQF-COSY) experiments, the cross-peaks resulting from deoxyribose ring conformation sensitive proton-proton vicinal couplings, i.e., all 1''-2'', 1''-2", 2''-3'', and 3''-4'' couplings and six from 2"-3'' couplings, were observed. From the cross-peak find structure, the 2'',2" proton assignments can be confirmed; coupling constants J1''2'' and J1''2" and sums of coupling constants involving H2'' and H2" for all residues and H3'' for C8 were obtained. The DISCO procedure [Kessler, H., Muller, A., and Oschkinat, H. (1985) Magn. Reson. Chem. 23, 844-852] was used to extract individual 1''-2'' and 1''-2" coupling constants. The sum of coupling constants involving H1'' or H3'' was measured from the one-dimensional spectrum where signal overlap is not a problem. Analysis of the resulting coupling constants and sums of coupling constants, in the manner of Rinkel and Altona [Rinkel, L. J., and Altona, C. (1987) J. Biomol. Struct. Dyn. 4, 621-649], led to the following conclusion: C2''-endo deoxyribose ring conformation is predominant for every residue, but a significant amount of C3''-endo conformation may exist, ranging from 14% to 30%.

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