Hu L T, Perides G, Noring R, Klempner M S
Division of Geographic Medicine and Infectious Diseases, Tufts University School of Medicine, New England Medical Center, Boston, Massachusetts 02111, USA.
Infect Immun. 1995 Sep;63(9):3491-6. doi: 10.1128/iai.63.9.3491-3496.1995.
We studied the binding of plasminogen to Borrelia burgdorferi, a spirochete which causes Lyme disease and produces no endogenous proteases which digest extracellular matrix proteins. Using 125I-labeled plasminogen, we demonstrated that B. burgdorferi bound human plasminogen and that this binding was inhibitable with unlabeled plasminogen. 125I-labeled plasminogen binding by B. burgdorferi was also inhibited by the lysine analog epsilon-aminocaproic acid. There was no significant difference in the binding of Glu- or Lys-plasminogen to B. burgdorferi. Binding of plasminogen was similar in low-passage (infectious) and high-passage (noninfectious) isolates of B. burgdorferi. Plasminogen bound to the surface of B. burgdorferi could be converted into plasmin by a human urokinase-type plasminogen activator. 125I-labeled plasminogen ligand blots of borrelial membrane proteins demonstrated two prominent binding proteins at approximately 70 and approximately 30 kDa. By Western blot (immunoblot), the 30-kDa protein was found to be outer surface protein A (Osp A) of B. burgdorferi. 125I-labeled plasminogen binding to both the 70-kDa protein and Osp A was inhibited by approximately 90% with a 1,000-fold excess of unlabeled plasminogen. By scanning densitometry, the 70-kDa band bound > 10 time more 125I-labeled plasminogen than did Osp A. An Osp A-deficient mutant of B. burgdorferi and wild-type B. burgdorferi bound equal amounts of 125I-labeled plasminogen. Ligand blots of membrane proteins from an Osp A-deficient mutant showed association of 125I-labeled plasminogen at only the 70-kDa protein. Two-dimensional gel electrophoresis showed that the 70-kDa protein had a pI of approximately 5.3, clearly separable from Osp A. The association of host plasmin(ogen) with borrelial surface proteins provides a mechanism by which B. burgdorferi can digest extracellular matrix and disseminate.
我们研究了纤溶酶原与伯氏疏螺旋体的结合情况，伯氏疏螺旋体是一种可引发莱姆病的螺旋体，它不产生能消化细胞外基质蛋白的内源性蛋白酶。我们使用¹²⁵I标记的纤溶酶原，证明了伯氏疏螺旋体能够结合人纤溶酶原，且这种结合可被未标记的纤溶酶原抑制。赖氨酸类似物ε-氨基己酸也能抑制伯氏疏螺旋体对¹²⁵I标记纤溶酶原的结合。谷氨酸纤溶酶原或赖氨酸纤溶酶原与伯氏疏螺旋体的结合没有显著差异。在低传代（有感染性）和高传代（无感染性）的伯氏疏螺旋体分离株中，纤溶酶原的结合情况相似。结合在伯氏疏螺旋体表面的纤溶酶原可被人尿激酶型纤溶酶原激活剂转化为纤溶酶。伯氏疏螺旋体膜蛋白的¹²⁵I标记纤溶酶原配体印迹显示，在大约70 kDa和大约30 kDa处有两种显著的结合蛋白。通过蛋白质免疫印迹法（免疫印迹）发现，30 kDa的蛋白是伯氏疏螺旋体的外表面蛋白A（Osp A）。用过量1000倍的未标记纤溶酶原可使¹²⁵I标记纤溶酶原与70 kDa蛋白和Osp A的结合均被抑制约90%。通过扫描密度测定法，70 kDa条带结合的¹²⁵I标记纤溶酶原比Osp A多10倍以上。伯氏疏螺旋体的Osp A缺陷突变体和野生型伯氏疏螺旋体结合等量的¹²⁵I标记纤溶酶原。Osp A缺陷突变体的膜蛋白配体印迹显示，¹²⁵I标记纤溶酶原仅与70 kDa蛋白结合。二维凝胶电泳显示，70 kDa蛋白的等电点约为5.3，与Osp A明显可分离。宿主纤溶酶（原）与伯氏疏螺旋体表面蛋白的结合提供了一种机制，通过该机制伯氏疏螺旋体能够消化细胞外基质并扩散。
