title: Isolation of new phosphorylated glycoprotein from mineralized phase of bone that exhibits limited homology to adhesive protein osteopontin.
abstract: Extracts of the mineralized phase of rat calvaria were shown to contain bone acidic glycoprotein-75, a new phosphorylated glycoprotein which co-purifies with small bone proteoglycans through anion-exchange chromatography. Final purification of each was brought about with a subsequent hydroxyapatite step. Bone acidic glycoprotein-75 is 75,000 in molecular weight with a 29.3% molar content of acidic amino acid residues, a 7.0% (w/w) content of sialic acid, and a 7.9% molar content of organic phosphate. Its N-terminal sequence was determined as Leu-Pro-Val-Ala-Arg-Tyr-Gln-Asn-Thr-Glu-Glu-Glu-Glu-. Because the size and charge density properties of bone acidic glycoprotein-75 are similar to those reported for rat bone sialoprotein II, calvarial sialoprotein II was also purified to homogeneity, and its amino acid composition and N-terminal sequence were determined. The sequence results showed an identity with the first 5 residues of human sialoprotein II and a complete lack of homology with bone acidic glycoprotein-75, which, furthermore, did not bind anti-sialoprotein II antibodies. Although the N-terminal sequence of bone acidic glycoprotein-75 appears to be unique, a 33% homology is shared with rat adhesive protein osteopontin. Affinity-purified antibodies against osteopontin were found to specifically bind to bone acidic glycoprotein-75 and to sialoprotein II upon immunoblotting, whether as purified proteins or as components of crude calvarial extracts. In summary, bone acidic glycoprotein-75 is a new phosphorylated glycoprotein from the mineralized compartment of rat calvarial tissue with a limited structural homology to osteopontin.
authors.affiliation: Division of Molecular Biology and Biochemistry, School of Basic Life Sciences, University of Missouri-Kansas City 64110.
authors.forename: J P
authors.initials: JP
authors.lastname: Gorski
authors.forename: K
authors.initials: K
authors.lastname: Shimizu
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001842:Bone and Bones / Q000032:analysis*; D002845:Chromatography; D002852:Chromatography, Ion Exchange; D017886:Durapatite; D006023:Glycoproteins / Q000302:isolation & purification*; D006801:Humans; D006882:Hydroxyapatites; D008969:Molecular Sequence Data; D008970:Molecular Weight; D053495:Osteopontin; D010750:Phosphoproteins / Q000302:isolation & purification*; D011509:Proteoglycans / Q000302:isolation & purification; D051381:Rats; D011919:Rats, Inbred Strains; D012689:Sequence Homology, Nucleic Acid; D012795:Sialoglycoproteins
chemical_list: D000596:Amino Acids; D006023:Glycoproteins; D006882:Hydroxyapatites; D010750:Phosphoproteins; D011509:Proteoglycans; C506895:SPP1 protein, human; D012795:Sialoglycoproteins; C506897:Spp1 protein, rat; D053495:Osteopontin; D017886:Durapatite