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Journal of Bacteriology, July 1999, p. 4420-4423, Vol. 181, No. 14
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Physicochemical Evidence that Treponema pallidum TroA Is a Zinc-Containing Metalloprotein That Lacks Porin-Like Structure

Ranjit K. Deka,1 Yong-Hwan Lee,2 Kayla E. Hagman,1 Dmitriy Shevchenko,2 Clifford A. Lingwood,3 Charles A. Hasemann,2 Michael V. Norgard,1 and Justin D. Radolf1,2,*

Departments of Microbiology1 and Internal Medicine,2 The University of Texas Southwestern Medical Center, Dallas, Texas 75235, and the Division of Research Microbiology, Research Institute, Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada3

Received 30 November 1998/Accepted 3 May 1999

Although TroA (Tromp1) was initially reported to be a Treponema pallidum outer membrane protein with porin-like properties, subsequent studies have suggested that it actually is a periplasmic substrate-binding protein involved in the transport of metals across the treponemal cytoplasmic membrane. Here we conducted additional physicochemical studies to address the divergent viewpoints concerning this protein. Triton X-114 phase partitioning of recombinant TroA constructs with or without a signal sequence corroborated our prior contention that the native protein's amphiphilic behavior is due to its uncleaved leader peptide. Whereas typical porins are trimers with extensive beta -barrel structure, size exclusion chromatography and circular dichroism spectroscopy revealed that TroA was a monomer and predominantly alpha-helical. Neutron activation, atomic absorption spectroscopy, and anomalous X-ray scattering all demonstrated that TroA binds zinc in a 1:1 molar stoichiometric ratio. TroA does not appear to possess structural features consistent with those of bacterial porins.

* Corresponding author. Present address: Center for Microbial Pathogenesis, University of Connecticut Health Center, MC 3710, School of Medicine, 263 Farmington Ave., Farmington, CT 06030. Phone: (860) 679-8129. Fax: (860) 679-8130. E-mail: Jradolf{at}up.uchc.edu.

Journal of Bacteriology, July 1999, p. 4420-4423, Vol. 181, No. 14
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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