Mapping Tight Junction Architecture

Project Summary Endothelia and epithelia throughout the body rely on macromolecular complexes known as tight junctions to modulate tissue barrier selectivity, proliferation, and polarity. Tight junctions are intercellular adhesion complexes that form strands around the apical side of cell-cell junctions. Tight junctions act as barriers that protect organs from pathogens while simultaneously allowing for the selective passage of nutrients, which establishes the chemical microenvironments of all tissue compartments. Thus, tight junction dysregulation is a hallmark of many human diseases. According to prevailing models, tight junctions assemble around oligomeric strands of claudin integral membrane proteins. The properties and stoichiometry of these strands are then augmented by the integral membrane protein occludin and the peripheral membrane protein ZO-1. To date, no direct observation of the interaction of tight junction subunits has been observed to support these models. This is a major gap in our understanding of how the chemical microenvironments in all tissue systems are established, and a roadblock in therapeutic intervention. In this proposal, using an approach integrating structural biology, cell biology, and physiology, we will uncover the structural determinants of tight junction function through elucidating the mechanisms of claudin oligomerization, claudin barrier function, and how tight junction subunits assemble with claudins to tune tight junction function.