title: Posttranslational modifications to human bone sialoprotein determined by mass spectrometry.
abstract: Bone sialoprotein (BSP) is an acidic 301 amino acid protein expressed by osteoblasts and at a low level by hypertrophic chondrocytes. Its expression is highest during early stages of bone formation, and it is particularly abundant in the cells lining the surface of newly formed trabeculae. BSP contains numerous substituents which are anionic in nature and apparently essential for the function of the protein. Thus, the proposed role of BSP in hydroxyapatite nucleation and growth may depend on such modifying groups. The posttranslational modifications include several acidic oligosaccharides as well as phosphate and sulfate groups. This work combines matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry with selective enzyme treatment of BSP to provide new information on the precise distribution and structure of oligosaccharides, sulfate, and phosphate groups in BSP isolated from human bone. The results provide a high level of detail in the location of these modifying groups toward the end of providing a basis for further understanding the function of BSP in bone nucleation.
authors.affiliation: Osiris Therapeutics, Inc., Baltimore, Maryland 21231, USA.
authors.forename: J
authors.initials: J
authors.lastname: Zaia
authors.forename: R
authors.initials: R
authors.lastname: Boynton
authors.forename: D
authors.initials: D
authors.lastname: Heinegård
authors.forename: F
authors.initials: F
authors.lastname: Barry
mesh_terms: D000328:Adult; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry; D000818:Animals; D002845:Chromatography; D002851:Chromatography, High Pressure Liquid; D010450:Endopeptidases / Q000378:metabolism; D006023:Glycoproteins / Q000737:chemistry; D006026:Glycoside Hydrolases / Q000378:metabolism; D006801:Humans; D058574:Integrin-Binding Sialoprotein; D013058:Mass Spectrometry; D008666:Metalloendopeptidases; D008969:Molecular Sequence Data; D009005:Monosaccharides / Q000378:metabolism; D009844:Oligosaccharides / Q000737:chemistry; D010710:Phosphates / Q000737:chemistry; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D012795:Sialoglycoproteins / Q000737:chemistry* / Q000378:metabolism; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013997:Time Factors; D014357:Trypsin / Q000494:pharmacology
chemical_list: D000596:Amino Acids; D006023:Glycoproteins; C546871:IBSP protein, human; D058574:Integrin-Binding Sialoprotein; D009005:Monosaccharides; D009844:Oligosaccharides; D010710:Phosphates; D012795:Sialoglycoproteins; D006026:Glycoside Hydrolases; D010450:Endopeptidases; D014357:Trypsin; D008666:Metalloendopeptidases; C058921:endoproteinase Asp-N