Kelm R J, Swords N A, Orfeo T, Mann K G
University of Vermont, Department of Biochemistry, College of Medicine, Burlington 05405.
J Biol Chem. 1994 Dec 2;269(48):30147-53.
Osteonectin is an adhesive glycoprotein synthesized constitutively by osteoblasts, endothelial cells, and megakaryocytes. Bone-derived and platelet-derived osteonectins differ in their electrophoretic mobility and carbohydrate content, and each displays different affinities for collagen matrices. Both types of osteonectin bind to plasminogen (Kd(app), of 4.7 +/- 1.0 x 10(-8) M for bone osteonectin and 1.2 +/- 0.1 x 10(-7) M for platelet osteonectin). The osteonectin-plasminogen interaction is inhibited by alpha 2-antiplasmin and epsilon-aminocaproic acid, suggesting that the interaction is mediated through the kringle 1 region of plasminogen. Both osteonectins enhance the rate of plasmin generation by tissue-type plasminogen activator to approximately the same extent as fibrinogen. Equilibrium binding measurements conducted using total internal reflection fluorescence spectroscopy indicate that plasminogen binds to collagen in the presence of bone osteonectin (Kd = 1.30 +/- 0.1 x 10(-7) M). No binding of plasminogen to collagen matrix was detected in the presence of platelet osteonectin or in the absence of bone osteonectin. Bone osteonectin-dependent binding of plasminogen to collagen matrix is reversed by the addition of epsilon-aminocaproic acid. The ability of both types of osteonectin to bind to and influence plasminogen activation and of bone osteonectin to anchor plasminogen on collagen matrices suggests that osteonectin may play a role in directing extracellular matrix proteolysis.
骨连接素是一种由成骨细胞、内皮细胞和巨核细胞组成性合成的黏附糖蛋白。骨源性和血小板源性骨连接素在电泳迁移率和碳水化合物含量上有所不同，并且它们对胶原基质表现出不同的亲和力。两种类型的骨连接素都能与纤溶酶原结合（骨源性骨连接素的Kd(app)为4.7±1.0×10⁻⁸M，血小板源性骨连接素的Kd(app)为1.2±0.1×10⁻⁷M）。骨连接素与纤溶酶原的相互作用受到α2-抗纤溶酶和ε-氨基己酸的抑制，这表明这种相互作用是通过纤溶酶原的kringle 1区域介导的。两种骨连接素都能将组织型纤溶酶原激活剂产生纤溶酶的速率提高到与纤维蛋白原大致相同的程度。使用全内反射荧光光谱进行的平衡结合测量表明，在骨源性骨连接素存在的情况下，纤溶酶原与胶原结合（Kd = 1.30±0.1×10⁻⁷M）。在血小板源性骨连接素存在的情况下或在没有骨源性骨连接素的情况下，未检测到纤溶酶原与胶原基质的结合。添加ε-氨基己酸可逆转骨源性骨连接素依赖性的纤溶酶原与胶原基质的结合。两种类型的骨连接素结合并影响纤溶酶原激活的能力以及骨源性骨连接素将纤溶酶原锚定在胶原基质上的能力表明，骨连接素可能在指导细胞外基质蛋白水解中发挥作用。
