Gonzalez-Gronow Mario, Kalfa Theodosia, Johnson Carrie E, Gawdi Govind, Pizzo Salvatore V
Department of Pathology, Duke University Medical Center, Durham, North Carolina 27710, USA.
J Biol Chem. 2003 Jul 18;278(29):27312-8. doi: 10.1074/jbc.M303172200. Epub 2003 May 7.
Human plasminogen contains structural domains that are termed kringles. Proteolytic cleavage of plasminogen yields kringles 1-3 or 4 and kringle 5 (K5), which regulate endothelial cell proliferation. The receptor for kringles 1-3 or 4 has been identified as cell surface-associated ATP synthase; however, the receptor for K5 is not known. Sequence homology exists between the plasminogen activator streptokinase and the human voltage-dependent anion channel (VDAC); however, a functional relationship between these proteins has not been reported. A streptokinase binding site for K5 is located between residues Tyr252-Lys283, which is homologous to the primary sequence of VDAC residues Tyr224-Lys255. Antibodies against these sequences react with VDAC and detect this protein on the plasma membrane of human endothelial cells. K5 binds with high affinity (Kd of 28 nm) to endothelial cells, and binding is inhibited by these antibodies. Purified VDAC binds to K5 but only when reconstituted into liposomes. K5 also interferes with mechanisms controlling the regulation of intracellular Ca2+ via its interaction with VDAC. K5 binding to endothelial cells also induces a decrease in intracellular pH and hyperpolarization of the mitochondrial membrane. These studies suggest that VDAC is a receptor for K5.
人纤溶酶原含有被称为kringle的结构域。纤溶酶原的蛋白水解切割产生kringle 1 - 3或4以及kringle 5（K5），它们调节内皮细胞增殖。已确定kringle 1 - 3或4的受体为细胞表面相关的ATP合酶；然而，K5的受体尚不清楚。纤溶酶原激活剂链激酶与人电压依赖性阴离子通道（VDAC）之间存在序列同源性；然而，尚未报道这些蛋白质之间的功能关系。K5的链激酶结合位点位于Tyr252 - Lys283残基之间，这与VDAC残基Tyr224 - Lys255的一级序列同源。针对这些序列的抗体与VDAC反应，并在人内皮细胞的质膜上检测到该蛋白。K5以高亲和力（解离常数为28 nM）与内皮细胞结合，并且这种结合被这些抗体抑制。纯化的VDAC与K5结合，但仅在重构到脂质体中时才结合。K5还通过与VDAC的相互作用干扰控制细胞内Ca2+调节的机制。K5与内皮细胞的结合还会导致细胞内pH值降低和线粒体膜超极化。这些研究表明VDAC是K5的受体。
