Haverstick D M, Dixit V M, Grant G A, Frazier W A, Santoro S A
Biochemistry. 1985 Jun 18;24(13):3128-34. doi: 10.1021/bi00334a009.
Thrombospondin (TSP) is a glycoprotein secreted from the alpha-granules of platelets upon activation. In the presence of divalent cations, the secreted protein binds to the surface of the activated platelets and is responsible for the endogenous lectin-like activity associated with activated platelets. Platelets fixed with formaldehyde following activation by thrombin are agglutinated by exogenously added TSP. Fixed, nonactivated platelets are not agglutinated. The platelet agglutinating activity of TSP is optimally expressed in the presence of 2 mM each of Mg2+ and Ca2+. Reduction of the disulfide bonds within the TSP molecule inhibits its platelet agglutinating activity. TSP bound to the surface of fixed, activated platelets can be eluted by the addition of disodium ethylenediaminetetraacetate. This approach was exploited to identify the region of the TSP molecule containing the platelet binding site. The binding site resides within a thermolytic fragment of TSP with Mr 140 000 but is not present in the Mr 120 000 fragment derived from the polypeptide of Mr 140 000. Since both the Mr 140 000 and 120 000 fragments contain fibrinogen binding sites, this finding suggests that the binding of TSP to the platelet surface requires interaction with other platelet surface components in addition to fibrinogen. The observation that fibrinogen only partially inhibits the TSP-mediated agglutination of fixed, activated platelets is consistent with this interpretation.
血小板反应蛋白（TSP）是血小板激活后从α颗粒分泌的一种糖蛋白。在二价阳离子存在的情况下，分泌的蛋白质会结合到活化血小板的表面，并负责与活化血小板相关的内源性凝集素样活性。经凝血酶激活后用甲醛固定的血小板会被外源性添加的TSP凝集。固定的、未活化的血小板则不会发生凝集。TSP的血小板凝集活性在Mg2+和Ca2+各为2 mM的情况下最佳表达。TSP分子内二硫键的减少会抑制其血小板凝集活性。结合在固定的活化血小板表面的TSP可通过添加乙二胺四乙酸二钠洗脱。利用这种方法来确定TSP分子中包含血小板结合位点的区域。结合位点位于Mr 140 000的TSP热解片段内，但不存在于源自Mr 140 000多肽的Mr 120 000片段中。由于Mr 140 000和120 000片段都含有纤维蛋白原结合位点，这一发现表明TSP与血小板表面的结合除了纤维蛋白原外，还需要与其他血小板表面成分相互作用。纤维蛋白原仅部分抑制TSP介导的固定活化血小板凝集这一观察结果与这一解释一致。
