Characterization of fetal porcine bone sialoproteins, secreted phosphoprotein I (SPPI, osteopontin), bone sialoprotein, and a 23-kDa glycoprotein. Demonstration that the 23-kDa glycoprotein is derived from the carboxyl terminus of SPPI.

摘要: Demineralizing extracts of porcine bone contain two large 66-80-kDa sialoproteins and smaller 20- 23-kDa glycoproteins with similar chemical properties. Each protein was characterized following extraction from fetal calvariae purification under dissociative conditions using Sepharose CL-6B, followed by fast liquid chromatography fractionation on hydroxyapatite Mono Q resins. Unlike the sialoproteins, did not sialic acid. Nevertheless, affinity-purified antibodies raised against recognized both 20-kDa a 67-kDa sialoprotein immunoblots. These also immunoprecipitated 60-kDa [35S]methionine-labeled produced cell-free synthesis calvarial mRNA, indicating that proteins were derived protein. The shown primary sequence analysis to be secreted phosphoprotein I (SPPI, osteopontin, I) (BSP, II). SPPI its susceptibility thrombin which fragment, glycoprotein isolated, 30-kDa fragment. Amino-terminal 23- revealed these carboxyl-terminal half molecule, showing 58% identity human rat, 50% mouse, sequences. Both appeared generated activity an endogenous trypsin-like protease cleaves at Arg-Ser (residues 155-156) Lys-Ala 182-183) bonds. Radiolabeling studies performed in vitro showed fragment detectable mineralized tissue within 4 h. phosphorylated but, unlike SPPI, sulfated. rapid generation presence different tissues developmental stages indicate fragmentation is important formation remodeling.