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Journal of Bacteriology, February 2006, p. 1251-1259, Vol. 188, No. 4
0021-9193/06/$08.00+0     doi:10.1128/JB.188.4.1251-1259.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Archaeal and Bacterial SecD and SecF Homologs Exhibit Striking Structural and Functional Conservation

Nicholas J. Hand,§ Reinhard Klein,{dagger} Anke Laskewitz,{ddagger} and Mechthild Pohlschröder*

Department of Biology, University of Pennsylvania, 201 Leidy Laboratories, 415 South University Ave., Philadelphia, Pennsylvania 19104

Received 25 October 2005/ Accepted 17 November 2005

The majority of secretory proteins are translocated into and across hydrophobic membranes via the universally conserved Sec pore. Accessory proteins, including the SecDF-YajC Escherichia coli membrane complex, are required for efficient protein secretion. E. coli SecDF-YajC has been proposed to be involved in the membrane cycling of SecA, the cytoplasmic bacterial translocation ATPase, and in the stabilizing of SecG, a subunit of the Sec pore. While there are no identified archaeal homologs of either SecA or SecG, many archaea possess homologs of SecD and SecF. Here, we present the first study that addresses the function of archaeal SecD and SecF homologs. We show that the SecD and SecF components in the model archaeon Haloferax volcanii form a cytoplasmic membrane complex in the native host. Furthermore, as in E. coli, an H. volcanii {Delta}secFD mutant strain exhibits both severe cold sensitivity and a Sec-specific protein translocation defect. Taken together, these results demonstrate significant functional conservation among the prokaryotic SecD and SecF homologs despite the distinct composition of their translocation machineries.

* Corresponding author. Mailing address: Department of Biology, University of Pennsylvania, 201 Leidy Laboratories, 415 South University Ave., Philadelphia, PA 19104. Phone: (215) 573-2283. Fax: (215) 898-8780. E-mail: pohlschr{at}sas.upenn.edu.

§ The Children's Hospital of Pennsylvania, Abramson Research Center, 3615 Civic Center Blvd., Suite 1004D, Philadelphia, PA 19104-4399.

{dagger} Present address: VBC-Genomics, Rennweg 96B, A-1030 Vienna, Austria.

{ddagger} Present address: University of Groningen, Department of Biology, Kerklaan 30, 9750 AA Haren, The Netherlands.

Journal of Bacteriology, February 2006, p. 1251-1259, Vol. 188, No. 4
0021-9193/06/$08.00+0     doi:10.1128/JB.188.4.1251-1259.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.





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