Journal of Bacteriology, November 2001, p. 6253-6264, Vol. 183, No. 21
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.21.6253-6264.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Department of Biochemistry, Microbiology, and Immunology1 and Centre for Research in Biopharmaceuticals,4 University of Ottawa, Ottawa, Ontario, Canada K1H 8M5; Department of Biology, University of Ottawa, Ottawa, Ontario, Canada K1N 6N52; and Protein Engineering Centres of Excellence, Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H73
Received 30 March 2001/Accepted 10 August 2001
The Min proteins are involved in determining cell division sites in bacteria and have been studied extensively in rod-shaped bacteria. We have recently shown that the gram-negative coccus Neisseria gonorrhoeae contains a min operon, and the present study investigates the role of minD from this operon. A gonococcal minD insertional mutant, CJSD1, was constructed and exhibited both grossly abnormal cell division and morphology as well as altered cell viability. Western blot analysis verified the absence of MinD from N. gonorrhoeae (MinDNg) in this mutant. Hence, MinDNg is required for maintaining proper cell division and growth in N. gonorrhoeae. Immunoblotting of soluble and insoluble gonococcal cell fractions revealed that MinDNg is both cytosolic and associated with the insoluble membrane fraction. The joint overexpression of MinCNg and MinDNg from a shuttle vector resulted in a significant enlargement of gonococcal cells, while cells transformed with plasmids encoding either MinCNg or MinDNg alone did not display noticeable morphological changes. These studies suggest that MinDNg is involved in inhibiting gonococcal cell division, likely in conjunction with MinCNg. The alignment of MinD sequences from various bacteria showed that the proteins are highly conserved and share several regions of identity, including a conserved ATP-binding cassette. The overexpression of MinDNg in wild-type Escherichia coli led to cell filamentation, while overexpression in an E. coli minD mutant restored a wild-type morphology to the majority of cells; therefore, gonococcal MinD is functional across species. Yeast two-hybrid studies and gel-filtration and sedimentation equilibrium analyses of purified His-tagged MinDNg revealed a novel MinDNg self-interaction. We have also shown by yeast two-hybrid analysis that MinD from E. coli interacts with itself and with MinDNg. These results indicate that MinDNg is required for maintaining proper cell division and growth in N. gonorrhoeae and suggests that the self-interaction of MinD may be important for cell division site selection across species.
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