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背景
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Fetuin A (from the Latin word fetus for offspring; also alpha 2-HS [Heremans and Schmid] glycoprotein/AHSG, 59 kDa BSP and pp63) is a 59-63 kDa soluble, highly glycosylated type 3 member of the fetuin family of proteins. Originally isolated from fetal calf serum, rat fetuin A is now reported to be secreted by hepatocytes and, possibly, osteoblasts. Functionally, fetuin A appears to complex with matrix Gla protein, bind calcium phosphate and to regulate matrix mineralization. While it does not dissolve existing mineral, it does inhibit unwarranted tissue mineralization and the inflammatory reaction that accompanies it. A role for fetuin A in the regulation of insulin receptor signaling is unclear. Mature rat fetuin A is 334 amino acids (aa) in length. It contains two cystatin fetuin A type I domains (aa 19-133 and 144-250) that control mineralization, and a C-terminal domain (aa 255-352) that may interact with the insulin receptor. There are at least four utilized phosphorylation sites at Ser138, 313, 316 and 318, and one potential internal cleavage site between Arg143-Lys144 that, if utilized, would generate a disulfide-linked heterodimer. Mature rat fetuin A shares 85% and 61% aa sequence identity with mouse and human fetuin A, respectively.
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