Lowrance J H, Hasty D L, Simpson W A
Veterans Administration Medical Center, Memphis, Tennessee 38104.
Infect Immun. 1988 Sep;56(9):2279-85. doi: 10.1128/iai.56.9.2279-2285.1988.
The adherence of Streptococcus sanguis to specific receptors exposed or deposited at the site of endothelial damage may play an important role in the development of infective endocarditis. Adherence of the Challis strain of S. sanguis to gelatin (or collagen) and gelatin-binding components of plasma was examined with an enzyme-linked immunosorbent assay. S. sanguis adhered poorly to immobilized gelatin and to molecular or fibrillar collagen. However, in the presence of fresh human plasma, the adherence of S. sanguis to all three substrates increased as much as eightfold. Removal of gelatin-binding proteins eliminates the ability of plasma to enhance adherence of S. sanguis to the substrates. Addition of purified human plasma fibronectin (Fn) to the absorbed plasma restored the adherence-promoting ability in a dose-dependent manner. A similar dose-dependent increase in S. sanguis adherence was observed when increasing concentrations of Fn alone were added to the gelatin-coated assay wells. S. sanguis adherence to immobilized fibronectin could not be inhibited by preincubating either the bacteria or the gelatin-coated assay wells with Fn or by including excess soluble Fn in the assay mixture. Studies with peptides purified from trypsin digests of Fn indicated that the 160- to 180-kilodalton (kDa) fragments which retain both the gelatin-binding and the cell-binding regions of the intact molecule support adherence of S. sanguis to gelatin. The 160- to 180-kDa fragments inhibited the interaction of S. sanguis with immobilized Fn. In contrast, intact Fn and the 31-kDa amino-terminal fragment were unable to inhibit the adherence when used in equivalent or greater molar amounts. These in vitro results suggest that in the presence of whole plasma, S. sanguis binds to immobilized gelatin or collagen via Fn bound to the immobilized substrates. Our finding that adherence of S. sanguis to immobilized Fn can occur in the presence of large concentrations of Fn, whether in plasma or purified, indicates that a S. sanguis-binding domain is cryptic in the Fn molecule while in solution and is exposed by a conformational change when the Fn becomes bound to gelatin-coated plastic. The ability of peptide fragments of Fn to inhibit S. sanguis adherence is consistent with this hypothesis.
血链球菌粘附于在内皮损伤部位暴露或沉积的特定受体，这可能在感染性心内膜炎的发展过程中起重要作用。采用酶联免疫吸附测定法检测了血链球菌Challis菌株对明胶（或胶原蛋白）及血浆中明胶结合成分的粘附情况。血链球菌对固定化明胶和分子或纤维状胶原蛋白的粘附性较差。然而，在新鲜人血浆存在的情况下，血链球菌对所有三种底物的粘附增加了多达八倍。去除明胶结合蛋白会消除血浆增强血链球菌对底物粘附的能力。向吸附的血浆中添加纯化的人血浆纤连蛋白（Fn）可按剂量依赖性方式恢复其促进粘附的能力。当向包被明胶的检测孔中单独添加浓度不断增加的Fn时，也观察到血链球菌粘附呈类似的剂量依赖性增加。预先用Fn孵育细菌或包被明胶的检测孔，或者在检测混合物中加入过量的可溶性Fn，均不能抑制血链球菌对固定化纤连蛋白的粘附。对从Fn胰蛋白酶消化物中纯化的肽段进行的研究表明，保留完整分子明胶结合区和细胞结合区的160至180千道尔顿（kDa）片段支持血链球菌对明胶的粘附。160至180 kDa片段抑制了血链球菌与固定化Fn的相互作用。相比之下，完整的Fn和31 kDa氨基末端片段以等量或更大摩尔量使用时无法抑制粘附。这些体外结果表明，在全血浆存在的情况下，血链球菌通过与固定化底物结合的Fn与固定化明胶或胶原蛋白结合。我们的发现表明，无论在血浆中还是纯化状态下，在高浓度Fn存在时血链球菌仍能粘附于固定化Fn，这表明血链球菌结合结构域在Fn分子处于溶液状态时是隐蔽的，而当Fn与包被明胶的塑料结合时会因构象变化而暴露。Fn肽段抑制血链球菌粘附的能力与这一假设一致。
