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Journal of Bacteriology, July 2008, p. 4880-4887, Vol. 190, No. 14
0021-9193/08/$08.00+0     doi:10.1128/JB.00412-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

ATPase Activity of Mycobacterium tuberculosis SecA1 and SecA2 Proteins and Its Importance for SecA2 Function in Macrophages{triangledown}

Jie M. Hou,1 Nadia G. D'Lima,1 Nathan W. Rigel,2 Henry S. Gibbons,2,{dagger} Jessica R. McCann,2 Miriam Braunstein,2* and Carolyn M. Teschke1*

Department of Molecular and Cell Biology, University of Connecticut, Storrs, Connecticut 06269-3125,1 Department of Microbiology and Immunology, School of Medicine, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-72902

Received 24 March 2008/ Accepted 6 May 2008

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.

* Corresponding author. Mailing address for C. Teschke: Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT 06269-3125. Phone: (860) 486-4282. Fax: (860) 486-4331. E-mail: teschke{at}uconn.edu. Mailing address for M. Braunstein: Department of Microbiology and Immunology, School of Medicine, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7290. Phone: (919) 966-5051. Fax: (919) 962-8103. E-mail: braunste{at}med.unc.edu

{triangledown} Published ahead of print on 16 May 2008.

{dagger} Present address: Edgewood Chemical Biological Center, Aberdeen Proving Ground, MD 21010.

Journal of Bacteriology, July 2008, p. 4880-4887, Vol. 190, No. 14
0021-9193/08/$08.00+0     doi:10.1128/JB.00412-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



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