Hou Jie M, D'Lima Nadia G, Rigel Nathan W, Gibbons Henry S, McCann Jessica R, Braunstein Miriam, Teschke Carolyn M
Department of Molecular and Cell Biology, University of Connecticut, Storrs, Connecticut 06269-3125, USA.
J Bacteriol. 2008 Jul;190(14):4880-7. doi: 10.1128/JB.00412-08. Epub 2008 May 16.
The Sec-dependent translocation pathway that involves the essential SecA protein and the membrane-bound SecYEG translocon is used to export many proteins across the cytoplasmic membrane. Recently, several pathogenic bacteria, including Mycobacterium tuberculosis, were shown to possess two SecA homologs, SecA1 and SecA2. SecA1 is essential for general protein export. SecA2 is specific for a subset of exported proteins and is important for M. tuberculosis virulence. The enzymatic activities of two SecA proteins from the same microorganism have not been defined for any bacteria. Here, M. tuberculosis SecA1 and SecA2 are shown to bind ATP with high affinity, though the affinity of SecA1 for ATP is weaker than that of SecA2 or Escherichia coli SecA. Amino acid substitution of arginine or alanine for the conserved lysine in the Walker A motif of SecA2 eliminated ATP binding. We used the SecA2(K115R) variant to show that ATP binding was necessary for the SecA2 function of promoting intracellular growth of M. tuberculosis in macrophages. These results are the first to show the importance of ATPase activity in the function of accessory SecA2 proteins.
依赖Sec的转运途径涉及必需的SecA蛋白和膜结合的SecYEG转运体，用于将许多蛋白质转运穿过细胞质膜。最近，包括结核分枝杆菌在内的几种病原菌被证明拥有两种SecA同源物，即SecA1和SecA2。SecA1对一般蛋白质输出至关重要。SecA2对一部分输出蛋白具有特异性，对结核分枝杆菌的毒力很重要。对于任何细菌，来自同一微生物的两种SecA蛋白的酶活性都尚未明确。在此，研究表明结核分枝杆菌的SecA1和SecA2与ATP具有高亲和力结合，尽管SecA1对ATP的亲和力弱于SecA2或大肠杆菌SecA。用精氨酸或丙氨酸取代SecA2的沃克A基序中保守的赖氨酸的氨基酸取代消除了ATP结合。我们使用SecA2(K115R)变体表明，ATP结合对于SecA2促进结核分枝杆菌在巨噬细胞内生长的功能是必需的。这些结果首次表明ATP酶活性在辅助性SecA2蛋白功能中的重要性。
