Physicochemical evidence that Treponema pallidum TroA is a zinc- containing metalloprotein that lacks porin-like structure

Ranjit K. Deka, Yong Hwan Lee, Kayla E. Hagman, Dmitriy Shevchenko, Clifford A. Lingwood, Charles A. Hasemann, Michael V. Norgard, Justin D. Radolf

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Abstract

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 β-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.

Original languageEnglish (US)
Pages (from-to)4420-4423
Number of pages4
JournalJournal of bacteriology
Volume181
Issue number14
StatePublished - Jul 1 1999

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ASJC Scopus subject areas

  • Microbiology
  • Molecular Biology

Cite this

Deka, R. K., Lee, Y. H., Hagman, K. E., Shevchenko, D., Lingwood, C. A., Hasemann, C. A., Norgard, M. V., & Radolf, J. D. (1999). Physicochemical evidence that Treponema pallidum TroA is a zinc- containing metalloprotein that lacks porin-like structure. Journal of bacteriology, 181(14), 4420-4423.