The oral cavity is the first critical interface between potentially harmful substances or pathogens in the hostenvironment, and evolution of the adaptive and innate immune defense mechanisms to inactivate or eliminatepathogenic microbes has to a great extent used protein-glycan interaction. The glycan components of salivahave been shown to play important roles in biological and immunological aspects of oral host-microbe, microbe-host, and microbe-microbe interactions, and we have shown that glycans attached salivary glycoproteins canact as a first line of host defense in the human mouth and that glycan recognition contributes to both colonizationand clearance of oral microbes. A revolutionary innovation in studies of protein-glycan interactions was theglycan microarray, which permitted the identification glycan ligands for biologically relevant glycan bindingproteins (GBP) by their simultaneous interrogation with hundreds of glycan structures printed on a microscopeslide. Comparisons of the structures of bound and non-bound glycans reveal the glycan specificity of GBP, andthis information is used in further biological studies to understand the biological function of GBP. In this projectwe will generate a glycan microarray composed of glycans that represent the salivary glycome, i.e. the entiretyof glycans in saliva. This will be accomplished by first producing a library of purified, naturally occurring N- andO-linked glycans released from 10 liters of pooled human saliva by an innovative process for the OxidativeRelease of Natural Glycans (ORNG) using simple household bleach. The library of glycans will be printed as aglycan microarray and interrogated with oral streptococcal glycan-binding adhesins to identify theircorresponding natural high-affinity glycan ligands. We will use our recently established toolbox of streptococcalserine-rich-repeat protein adhesins that each contain sialic-acid-binding Siglec-like domains of differingspecificity for subtypes of sialic acids in the wider context of their underlying subterminal glycans. For some ofthese lectins, the natural glycan ligands were not identified using currently available arrays, presumably due tothe absence of their corresponding natural glycan ligands presented in the assays to date. Since these are lectinsexpressed by oral microbes, we anticipate that there is a high probability that their natural glycan ligands will bepresent in the glycome of human saliva, the natural biological fluid in which these microorganisms thrive. ThisPhase I project should provide an example of how a complete glycome can be used as a discovery platform foridentifying a novel protein-glycan interaction. Once the details of the structure of the glycan ligand are defined,the information will become intellectual property that will lead to strategies to therapeutically interfere withmicrobial colonization or pathogen infection in the mouth and beyond. This platform for understanding theinteractions of oral microorganisms and extraoral systemic pathogens with the human may ultimately lead to thedevelopment of an improved artificial saliva, more closely mimicking the glycan landscape of natural humansaliva, as addition of human milk oligosaccharides has laid the groundwork for improvement of infant formula.
Public Health Relevance Statement: Project Narrative
In the oral cavity, saliva serves as the first critical interface between pathogens and their human host where
microbial surface-expressed protein adhesins bind to host glycans to initiate colonization. Glycans attached to
salivary proteins closely resemble those that pathogenic microbes encounter on their target tissues to initiate
infection. Evolution of host defense mechanisms likely has shaped glycans on salivary glycoproteins to make
them structurally analogous to host glycans as a decoy mechanism to prevent pathogens from binding to host
glycans on tissue surfaces. This project is designed to identify the precise salivary glycan ligands involved in this
process, and may lead to the development of an improved artificial saliva, more closely mimicking the glycan
landscape of natural human saliva.
Project Terms: <7S Gamma Globulin>
