JB Accepts, published online ahead of print on 16 May 2008

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J. Bacteriol. doi:10.1128/JB.00412-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

ATPase activity of Mycobacterium tuberculosis SecA1 and SecA2 proteins and its importance to SecA2 function in macrophages

Jie M. Hou, Nadia G. D'Lima, Nathan W. Rigel, Henry S. Gibbons, Jessica R. McCann, Miriam Braunstein^*, and Carolyn M. Teschke^*

Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT 06269-3125; Department of Microbiology and Immunology, School of Medicine, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7290; Edgewood Chemical Biological Center, Aberdeen Proving Ground, MD 21010

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 M. 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 E. coli SecA. Amino acid substitutions of the conserved lysine to arginine or alanine in the Walker A motif of SecA2 eliminated ATP binding. Using the SecA2 K115R variant, ATP binding was shown to be necessary for the SecA2 function in M. tuberculosis of promoting intracellular growth in macrophages. These results are the first to show the importance of ATPase activity in the function of accessory SecA2 proteins.

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