The temperature-sensitive hemagglutinin (Tsh) is an autotransporter protein secreted by avian-pathogenic Escherichia coli strains that colonize the respiratory tract and lead to airsacculitis, pericarditis, and colisepticemia. It is synthesized as a 140-kDa precursor protein, whose processing results in a 106-kDa passenger domain (Tshs) and a 33-kDa β-domain (Tshβ). The presence of a conserved 7-amino-acid serine protease motif within Tshs classifies the protein in a subfamily of autotransporters, known as serine protease autotransporters of the Enterobacteriaceae. In this study, we report that purified Tshs is capable of adhering to red blood cells, hemoglobin, and the extracellular matrix proteins fibronectin and collagen IV. We also demonstrate that Tshs exerts proteolytic activity against casein, and we provide experimental evidence demonstrating that serine 259 is essential for the protease function. However, this residue is not required for adherence to substrates, and its replacement by an alanine does not abolish binding activity. In summary, our results demonstrate that Tsh is a bifunctional protein with both adhesive and proteolytic properties.
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机译：对温度敏感的血凝素（Tsh）是由禽病原性 Escherichia coli 株分泌的一种自转运蛋白，其定植于呼吸道并导致气囊炎，心包炎和败血症。它被合成为一个140 kDa的前体蛋白，其加工过程产生一个106 kDa的客运结构域（Tsh s ）和一个33 kDa的β结构域（Tsh β）。 ）。 Tsh s 中存在一个保守的7个氨基酸的丝氨酸蛋白酶基序，可将该蛋白分类为自转运蛋白亚家族，称为肠杆菌科的丝氨酸蛋白酶自转运蛋白。在这项研究中，我们报道了纯化的Tsh s 能够与红细胞，血红蛋白以及细胞外基质蛋白纤连蛋白和胶原IV结合。我们还证明了Tsh s 对酪蛋白具有蛋白水解活性，并且我们提供了实验证据证明丝氨酸259对蛋白酶功能至关重要。然而，该残基对于粘附于底物不是必需的，并且其被丙氨酸替代不会消除结合活性。总而言之，我们的结果证明Tsh是具有粘附和蛋白水解特性的双功能蛋白。
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