Osteonectin cDNA sequence reveals potential binding regions for calcium and hydroxyapatite and shows homologies with both a basement membrane protein (SPARC) and a serine proteinase inhibitor (ovomucoid).

Abstract

Osteonectin is a prominent noncollagenous protein of developing bone. A 2150-base-pair cDNA coding for osteonectin, isolated from a bovine bone cell Agtll expression library, was sequenced and identified by comparison with protein sequence data. The nucleotide sequence predicts that osteonectin contains 304 amino acids, including a 17-residue signal peptide. Analysis of the deduced protein sequence suggests that the secreted protein contains at least four distinct structural domains. An acidic region at the amino terminus of the protein appears to be a potential hydroxyapatite-binding site. This is followed by a second domain, rich in cysteine, that shows sequence homology with cysteine-rich domains in turkey ovomucoid and other serine proteinase inhibitors. Two sequences homologous with central calcium-binding loops of "EF hands" and thus having potential to be high-affinity calcium-binding sites are located in two other domains within the carboxyl-terminal half of the protein. Finally, the osteonectin sequence shows near identity (>90%) with another protein, SPARC (secreted protein, acidic and rich in cysteine), secreted by mouse parietal endoderm. These data suggest that osteonectin, a protein present in bone and other selected tissues, is a multifunctional protein.

Molecular analysis of chicken embryo SPARC (osteonectin)

“…The identification of this second motif is based on revised consensus patterns in which all published sequences containing EF-hands have been taken into account (Bairoch, 1992). Bovine SPARC has also been described as having two EF-hands (Bolander et al, 1988). However, this site is not conserved in mouse (Engel et al, 1987) or frog (Damjanovski et al, 1992) and might not be functionally significant.…”

“…There is general agreement among investigators using either purified vertebrate SPARC (Sage and Bornstein, 1991), purified vertebrate BM-40 (Timpl, 1989), synthetic SPARC peptides (Lane and Sage, 1990;Sage, 1991, 1993;Hasselaar and Sage, 1992), purified BM-40 fragments , or recombinant BM-40 (Nischt et al, 1991). The collective data indicate a four-domain structure for this extracellular protein (Lankat-Buttgereit et al, 1988;Bolander et al, 1988;Engel et al, 1987).…”

“…SPARC was originally described as osteonectin, an abundant component of the extracellular matrix in bone (Tennine et al, 1981). The identity of these two proteins became apparent with the molecular cloning of the mouse (Mason et al, 1986), bovine (Bolander et al, 1988) and human cDNAs (Villameal et al, 1988). SPARC is also known as the basement membrane protein BM-40 (Dziadek et al, 1986;Lankat-Buttgereit, 1988), which binds to collagen types I-V in a calcium-dependent manner (Sage et al, 1989a;Lane and Sage, 1990;Mayer et al, 1991).…”

Osteopenia and decreased bone formation in osteonectin-deficient mice

“…The cDNA fragments were labeled with α-32 P-dCTP by random priming (Amersham Pharmacia Biotech, Piscataway, New Jersey, USA). The cDNAs used were bovine osteonectin, mouse bone sialoprotein, mouse osteo-pontin, rat fibronectin, rat α1(I) collagen, rat osteocalcin, mouse gelatinase B, human gelatinase A, rat collagenase-3, mouse VEGF, and rat GAPDH (23)(24)(25)(26)(27)(28)(29)(30)(31)(32). Hybridizations were carried out at 42°C in 50% formamide, 750 mM sodium chloride, 50 mM sodium phosphate, 5 mM EDTA, 5× Denhardt's solution, and 0.4% SDS (Sigma Chemical Co., St. Louis, Missouri, USA).…”

Characterization of Sparus aurata osteonectin cDNA and in silico analysis of protein conserved features: Evidence for more than one osteonectin in Salmonidae

“…Osteonectin has been identified in a number of evolutionary different species and analysis of available sequences has revealed high sequence conservation between species: more than 70% amino acid identity among vertebrates and around 40% between vertebrates and invertebrates [3]. Osteonectin is a single polypeptide chain composed of 4 distinct domains, containing numerous intramolecular disulfide bonds and undergoing posttranslational modification by N-linked glycosylation [7].…”