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Infect. Immun. doi:10.1128/IAI.00072-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Identification of transferrin binding domains in TbpB expressed by Neisseria gonorrhoeae

Department of Microbiology and Immunology, Virginia Commonwealth University Medical Center, Richmond, VA 23298-0678

^* To whom correspondence should be addressed. Email: cncornel{at}vcu.edu.

	Abstract

The transferrin iron acquisition system of N. gonorrhoeae is necessary for iron uptake from transferrin in the human host and requires the participation of two distinct proteins: TbpA and TbpB. TbpA is a TonB-dependent outer membrane transporter responsible for the transport of iron into the cell. TbpB is a lipid-modified protein, for which a precise role in receptor function has not yet been elucidated. These receptor complex proteins show promise as vaccine candidates; therefore, it is important to identify surface-exposed regions of the proteins required for wild-type functions. In this study we examined TbpB, which has been reported to be surface exposed in its entirety; however this hypothesis has never been tested experimentally. We placed the hemagglutinin (HA) epitope into TbpB with the dual purpose of examining surface exposure of particular epitopes as well as impacts on receptor function. Nine insertion mutants were created, placing the epitope downstream of the signal peptidase II cleavage site. We report that the HA epitope is surface accessible in all mutants, indicating that the full-length TbpB is completely surface exposed. By expressing the TbpB-HA fusion proteins in N. gonorrhoeae we were able to examine the impacts of each insertion on function of TbpB and the transferrin acquisition process. We propose that TbpB is comprised of two transferrin-binding competent lobes, both of which are critical for efficient iron uptake from human transferrin.