Exploring new virulence factors of the oral spirochete Treponema denticola

PROJECT SUMMARY Identification of bacterial virulence factors has been the epicenter in study of host-pathogen interactions. However, only a handful of virulence factors have been functionally characterized in the oral bacterium Treponema denticola (Td), an important and yet understudied oral pathobiont that is associated with periodontitis and other forms of oral infections. Growing evidence also shows that Td is implicated in systemic illnesses such as Alzheimer’s disease and oral cancer. During the last funding cycle, by using a multidisciplinary approach of genetics, biochemistry, cell biology, immunology, structural biology, and animal models, we have elucidated the role of TDE0362 (a cysteine protease), TDE0471 (a sialidase), and protein glycosylation in the pathophysiology of Td. Building upon this momentum, this renewal application focuses on sialidase and three newly identified virulence factors including a new cystalysin (TDE2410) and two filamentation-induced-by-cyclic-AMP (Fic) enzymes (TDE0061/TDE0233). Our preliminary results demonstrate that TDE2410 has hemolysin activity and TDE0061 and TDE0233 are toxic to both yeast and mammalian cells. Based on these results, we hypothesize that these newly identified virulence factors play critical roles in the pathophysiology of Td. To test this, three specific aims are proposed. Aim 1 seeks to investigate how Td employs sialidase to disarm the complement system and alter TLR2/TLR4-mediated innate immune response. If successful, it will improve our understanding of how bacterial pathogens modulate host innate immune defense via desialylation. Aim 2 focuses on cysteine metabolism and its role in Td. Cystalysin is a hallmark virulence factor of Td. It metabolizes cysteine producing pyruvate, ammonia, and H2S. Td lacks a de novo biosynthesis pathway of cysteine and thus needs exogenous cysteine for its growth. However, the mechanism by which Td acquires thiol amino acids remains elusive. We recently identified a putative cysteine transporter (TDE1668) and a new cystalysin (TDE2410). If successful, Aim 2 will provide mechanistic insights into understanding the role of cystalysins and cysteine metabolism in Td. Aim 3 proposes to elucidate the role of two Fic proteins in Td. Some bacterial pathogens have evolved a unique mechanism to hijack host signaling pathways (e.g., the Rho family of small GTPases) through Fic-mediated AMPylation, induce pathogenic effects, and promote bacterial infection. Thus far, Fic enzymes have not yet been studied in any oral pathogens. Therefore, the study in Aim 3 will open a new avenue to investigate the role of Fic proteins in oral pathogens. Completion of this project will not only advance Td research but also provide new directions and techniques to study other oral pathogens and their roles in the pathogenesis of periodontitis