Title : Identification of O-glycosylation
sites and partial characterization of
carbohydrate structure and disulfide linkages of human
insulin-like growth
factor binding protein 6
Abstract :
- The actions of insulin-like growth factors ( IGFs ) are modulated by a family of high-affinity binding proteins ( IGFBPs ), including IGFBP-6 , which preferentially binds IGF-II and is O-glycosylated
- Glycosylated and nonglycosylated recombinant human IGFBP-6 , expressed in Chinese hamster ovary cells and Escherichia coli, respectively, were purified using IGF-II affinity chromatography and reverse-phase medium-pressure chromatography
- Electrospray ionization mass spectrometry (ESMS) of glycosylated IGFBP-6 revealed considerable heterogeneity of carbohydrate composition
- Major glycoforms contained 8-16 monosaccharides , including N-acetylhexosamine, hexose, and N-acetylneuraminic acid.
- Glycosylation sites of IGFBP-6 were identified as Thr126, Ser144, Thr145, Thr146, and Ser152 by using a combination of ESMS and Edman sequencing of tryptic fragments separated by reverse-phase high-pressure liquid chromatography
- One oligosaccharide chain contained 5-6 monosaccharides , whereas the others contained 2-4 monosaccharides
- Glycosylated IGFBP-6 exhibited greater resistance to proteolysis by chymotrypsin and trypsin than nonglycosylated IGFBP-6
- Native disulfide bond positions in IGFBP-6 were localized by means of observed disulfide-linked tryptic fragments , revealing that there are two disulfide-linked subdomains within each of the N- and C-terminal regions and confirming a previous suggestion that the latter regions are not interconnected
- A model of IGFBP-6 is developed in which these distinct domains are separated by a central region which is O-glycosylated