Investigating the sweet side of gonorrhea to understand nutrient acquisition and sugar-based interactions with the host - The human-specific pathogen Neisseria gonorrhoeae (Ngo) causes the common sexually transmitted infection gonorrhea. Rapid evolution of drug resistance by Ngo has led to its identification as an urgent threat and emphasizes the need to identify an efficacious vaccine or more effective treatments. Our strategy to develop better therapeutics has focused on conserved outer membrane transport proteins that provide critical growth supporting functions during human infection. The outer membrane transport system (TbpA/B) that enables Ngo to employ human transferrin as an iron source is necessary for and produced during human infections. The highly conserved zinc transporters (TdfH and TdfJ) are also expressed in vivo. Potential drugs that target these receptors are expected to starve the bacteria of these essential nutrients. While the human protein ligands for these transport systems are known, we unexpectedly observed that these transporters also bind to distinct glycan moieties. Although transferrin is indeed glycosylated, the ligands for the zinc transporters, human calprotectin and human S100A7, are not glycan modified. This unanticipated observation led us to consider the novel concept that the outer membrane transporters serve other functions, potentially interacting with host cell glycan-modified proteins, in addition to enabling Ngo to overcome nutritional immunity. In this application, we propose interrogate the transporter-glycan interactions and assess whether these interactions are possibly “druggable”. We hypothesize that these TonB-dependent transporters (TdTs) serve additional host-specific functions (e.g., support nutrient transport or facilitate association with host cells) and that interference of TdT-glycan interactions will block Ngo infection of host cells. These studies are significant because identification of novel compounds to interfere with either nutrient acquisition or host cell interactions could lead to new insights into therapeutic interventions for an urgent threat pathogen that is close to being impossible to treat with existing drugs. These studies are innovative because our unexpected observation that the gonococcal outer membrane transporters also bind to distinct sugar residues raises the innovative possibility that these proteins are multi-functional and serve important functions in the context of host cell interaction, in addition to their known functions in nutrient acquisition. Other innovative aspects include the assembled team, the complementary approaches to be utilized, and the panel of unique reagents including monoclonal antibodies and drugs that could block critical TdT-dependent virulence functions including host cell interaction and nutrient acquisition. The specific aims of this new proposal are as follows. Aim 1: Determine the glycans/ligands that the TdTs interact with on host cells. Aim 2: Characterize the molecular details that define the TdT-glycan interactions. Aim 3: Investigate the ability of antibodies and compounds to block TdT-glycan interactions and TdT functions. Overall, these innovative studies will thoroughly interrogate the newly-recognized TdT-glycan interactions with a focus on interfering with key virulence characteristics contributed by these well conserved outer membrane transport systems.
