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Journal of Bacteriology, February 2009, p. 978-984, Vol. 191, No. 3
0021-9193/09/$08.00+0     doi:10.1128/JB.01321-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Maximal Efficiency of Coupling between ATP Hydrolysis and Translocation of Polypeptides Mediated by SecB Requires Two Protomers of SecA{triangledown}

Chunfeng Mao,1 Simon J. S. Hardy,1,2 and Linda L. Randall1*

Department of Biochemistry, University of Missouri, Columbia, Missouri 65211,1 Department of Biology, University of York, York YO10 5DD, United Kingdom2

Received 19 September 2008/ Accepted 25 October 2008

SecA is the ATPase that provides energy for translocation of precursor polypeptides through the SecYEG translocon in Escherichia coli during protein export. We showed previously that when SecA receives the precursor from SecB, the ternary complex is fully active only when two protomers of SecA are bound. Here we used variants of SecA and of SecB that populate complexes containing two protomers of SecA to different degrees to examine both the hydrolysis of ATP and the translocation of polypeptides. We conclude that the low activity of the complexes with only one protomer is the result of a low efficiency of coupling between ATP hydrolysis and translocation.

* Corresponding author. Mailing address: 117 Schweitzer Hall, University of Missouri, Columbia, MO 65211. Phone: (573) 884-4160. Fax: (573) 882-5635. E-mail: craneje{at}missouri.edu

{triangledown} Published ahead of print on 31 October 2008.

Journal of Bacteriology, February 2009, p. 978-984, Vol. 191, No. 3
0021-9193/09/$08.00+0     doi:10.1128/JB.01321-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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