High mobility group protein, HMG-1, contains insignificant glycosyl modification

High mobility group protein-1 (HMG-1) is a ubiquitous, highly conserved, and abundant nuclear protein. Recent findings suggest that HMG-1 may serve as a DNA chaperone protein and play a role in the regulation of transcription. There is a mounting interest in elucidating the mechanism by which HMG-1 protein takes part in these activities. HMG-1 has been reported to undergo an extensive array of posttranslational modifications, including glycosylation. We extend the earlier findings on the glycosylation of HMG-1 by quantitating the amount of carbohydrate on HMG-1 from calf thymus and chicken erythrocytes isolated by 2 different purification procedures. In addition, 2 different developmental stages (embryonic and adult) were examined in the chicken erythrocytes. The glycosyl composition was quantitated using the Dionex HPAE-PAD II system. Furthermore, the presence of O-linked GlcNAc on HMG-1 was determined by the enzymatic incorporation of 3H-galactose into HMG-1 protein. Contrary to earlier reports, less than 0.5 mol of total monosaccharides (Fuc, Man, GalNH2, GlcNH2, Gal) were detected per mole of HMG-1 protein, regardless of the source of the protein or the method of isolation. In addition, less than 0.002 mol of O-linked GlcNAc per mole of HMG-1 protein was detected. Thus, insignificant amount of glycosylation was found on HMG-1 protein. Because O-linked GlcNAc modification of proteins is believed to be a reversible posttranslational event, more definitive studies will need to be conducted before ruling out that the function of HMG-1 protein is not regulated by glycosylation.