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Journal of Bacteriology, April 2004, p. 2303-2308, Vol. 186, No. 8
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.8.2303-2308.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

The Tp38 (TpMglB-2) Lipoprotein Binds Glucose in a Manner Consistent with Receptor Function in Treponema pallidum

Ranjit K. Deka, Martin S. Goldberg, Kayla E. Hagman, and Michael V. Norgard*

Department of Microbiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390

Received 9 October 2003/ Accepted 31 December 2003

A 38-kDa lipoprotein of Treponema pallidum (Tp38) was predicted to be a periplasmic sugar-binding protein based on its sequence similarity to the glucose/galactose-binding (MglB) protein of Escherichia coli (P. S. Becker, D. R. Akins, J. D. Radolf, and M. V. Norgard, Infect. Immun. 62:1381-1391, 1994). Inasmuch as glucose is believed to be the principal, if not sole, carbon and energy source for T. pallidum and is readily available to the spirochete during its obligate infection of humans, we hypothesized that Tp38 may serve as the organism's requisite glucose receptor. For the present study, a nonacylated recombinant form of Tp38 was coexpressed with GroES and GroEL in E. coli to facilitate the isolation of soluble, properly folded Tp38. The highly sensitive method of intrinsic fluorescence spectroscopy, predicated on the manner in which tryptophan residues reside and move within protein microenvironments, was then used to assess sugar binding to Tp38. The intrinsic fluorescence of Tp38 was essentially unaltered when it was exposed to D-mannose, D-fucose, D-ribose, L-glucose, or L-galactose, but it changed markedly in the presence of D-glucose, and to a lesser extent, D-galactose, indicating binding. The Kd values for D-glucose and D-galactose binding to Tp38 were 152.2 ± 20.73 nM and 251.2 ± 55.25 nM, respectively. Site-directed mutagenesis of Trp-145, a residue postulated to contribute to the sugar-binding pocket in a manner akin to the essential Trp-183 in E. coli MglB, abolished Tp38's conformational change in response to D-glucose. The combined data are consistent with Tp38 serving as a glucose receptor for T. pallidum. These findings potentially have important implications for syphilis pathogenesis, particularly as they may pertain to glucose-mediated chemotactic responses by T. pallidum.

* Corresponding author. Mailing address: Department of Microbiology, UT Southwestern Medical Center, 6000 Harry Hines Blvd., Dallas, TX 75390-9048. Phone: (214) 648-5900. Fax: (214) 648-5905. E-mail: michael.norgard{at}utsouthwestern.edu.

Journal of Bacteriology, April 2004, p. 2303-2308, Vol. 186, No. 8
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.8.2303-2308.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Deka, R. K., Brautigam, C. A., Yang, X. F., Blevins, J. S., Machius, M., Tomchick, D. R., Norgard, M. V. (2006). The PnrA (Tp0319; TmpC) Lipoprotein Represents a New Family of Bacterial Purine Nucleoside Receptor Encoded within an ATP-binding Cassette (ABC)-like Operon in Treponema pallidum. J. Biol. Chem. 281: 8072-8081 [Abstract] [Full Text]  
  • LaFond, R. E., Lukehart, S. A. (2006). Biological Basis for Syphilis. Clin. Microbiol. Rev. 19: 29-49 [Abstract] [Full Text]  
  • Deka, R. K., Neil, L., Hagman, K. E., Machius, M., Tomchick, D. R., Brautigam, C. A., Norgard, M. V. (2004). Structural Evidence That the 32-Kilodalton Lipoprotein (Tp32) of Treponema pallidum Is an L-Methionine-binding Protein. J. Biol. Chem. 279: 55644-55650 [Abstract] [Full Text]  


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