Physicochemical evidence that Treponema pallidum TroA is a zinc-containing metalloprotein that lacks porin-like structure.
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.
Deka
R K
RK
Departments of Microbiology, The University of Texas Southwestern Medical Center, Dallas, Texas 75235, USA.
Lee
Y H
YH
Hagman
K E
KE
Shevchenko
D
D
Lingwood
C A
CA
Hasemann
C A
CA
Norgard
M V
MV
Radolf
J D
JD
D001426:Bacterial Proteins; D002942:Circular Dichroism; D008667:Metalloproteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017830:Octoxynol; D011092:Polyethylene Glycols; D018272:Porins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D013052:Spectrometry, X-Ray Emission; D013054:Spectrophotometry, Atomic; D014210:Treponema pallidum / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D015032:Zinc / Q000737:chemistry* / Q000378:metabolism*
D001426:Bacterial Proteins; D008667:Metalloproteins; D018272:Porins; C093836:Tromp1 protein, Treponema pallidum; D011092:Polyethylene Glycols; D017830:Octoxynol; C010615:Nonidet P-40; D015032:Zinc