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Journal of Bacteriology, June 2009, p. 3482-3491, Vol. 191, No. 11
0021-9193/09/$08.00+0     doi:10.1128/JB.00365-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Characterization of Streptococcus gordonii SecA2 as a Paralogue of SecA{triangledown} ,{dagger}

Barbara A. Bensing and Paul M. Sullam*

San Francisco Veterans Affairs Medical Center and the University of California, San Francisco, California

Received 16 March 2009/ Accepted 29 March 2009

The accessory Sec system of Streptococcus gordonii is essential for transport of the glycoprotein GspB to the bacterial cell surface. A key component of this dedicated transport system is SecA2. The SecA2 proteins of streptococci and staphylococci are paralogues of SecA and are presumed to have an analogous role in protein transport, but they may be specifically adapted for the transport of large, serine-rich glycoproteins. We used a combination of genetic and biochemical methods to assess whether the S. gordonii SecA2 functions similarly to SecA. Although mutational analyses demonstrated that conserved amino acids are essential for the function of SecA2, replacing such residues in one of two nucleotide binding folds had only minor effects on SecA2 function. SecA2-mediated transport is highly sensitive to azide, as is SecA-mediated transport. Comparison of the S. gordonii SecA and SecA2 proteins in vitro revealed that SecA2 can hydrolyze ATP at a rate similar to that of SecA and is comparably sensitive to azide but that the biochemical properties of these enzymes are subtly different. That is, SecA2 has a lower solubility in aqueous solutions and requires higher Mg2+ concentrations for maximal activity. In spite of the high degree of similarity between the S. gordonii paralogues, analysis of SecA-SecA2 chimeras indicates that the domains are not readily interchangeable. This suggests that specific, unique contacts between SecA2 and other components of the accessory Sec system may preclude cross-functioning with the canonical Sec system.

* Corresponding author. Mailing address: Division of Infectious Diseases, VA Medical Center (111W), 4150 Clement Street, San Francisco, CA 94121. Phone: (415) 221-4810, ext. 2550. Fax: (415) 750-6951. E-mail: paul.sullam{at}ucsf.edu

{triangledown} Published ahead of print on 10 April 2009.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

Journal of Bacteriology, June 2009, p. 3482-3491, Vol. 191, No. 11
0021-9193/09/$08.00+0     doi:10.1128/JB.00365-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

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