ALPHA-AND-BETA HSQC, AN HSQC-TYPE EXPERIMENT WITH IMPROVED RESOLUTIONFOR I2S GROUPS

A new HSQC-type pulse scheme is introduced that effectively improves t he spectral resolution by what corresponds to the size of geminal J(HH ) coupling constants, i.e., on the order of -14 Hz in CH2 groups of pe ptides and proteins. The gain in resolution comes from the fact that, in I2S groups with I-spin detection, only those resonances with the pa ssive I spin being in either the alpha or the beta state are excited. The experiment alpha&beta HSQC has two versions: one that is alpha and beta selective in the echo and antiecho parts, respectively, or the o pposite combination. This selection of polarizing only one half of the I-spin resonances works even when the two I spins are strongly couple d. Pure-absorption, selective alpha HSQC or beta HSQC spectra are obta ined by the two combinations of the echo part of one of the alpha&beta HSQC spectra with the antiecho part of the other. These two spectra ( alpha HSQC and beta HSQC) can be merged into another spectrum, Mab HSQ C, which has the appearance of an HSQC spectrum with homonuclear broad band decoupling of geminal scalar interactions. The method is demonstr ated on aqueous solutions of a decapeptide at the natural-abundance le vel of isotopes and on the protein rhodniin (103 residues) uniformly l abeled with C-13 and N-15. (C) 1996 Academic Press, Inc.