Rapid and simple approach for the NMR resonance assignment of the carbohydrate chains of an intact glycoprotein. Application of gradient-enhanced natural abundance 1H-13C HSQC and HSQC-TOCSY to the alpha-subunit of human chorionic gonadotropin.

The structure assessment of an intact glycoprotein in solution requires an extensive assignment of the carbohydrate NMR resonances. However, assignment of homonuclear spectra is very complicated because of the severe overlap of protein and carbohydrate signals. Application of pulsed field gradients allowed high quality natural abundance 1H-13C HSQC and HSQC-TOCSY spectra to be recorded of the alpha-subunit of human chorionic gonadotropin. Most carbohydrate 1H-13C correlations appear in a distinct region between the aromatic region and the protein C alpha-H alpha region. The enormous reduction in overlap led to fast and unambiguous assignment of the anomeric 1H-13C correlations. Subsequently, correlations of the monosaccharide skeleton atoms were readily assigned in the HSQC-TOCSY spectrum.