Single-Cell Biophysics: Measurement, Modulation, and Modeling

Single-Cell Biophysics: Measurement, Modulation, and Modeling

Saturday Speaker Abstracts

Nanoscale Architecture of Cadherin-based Cell Adhesions Pakorn Kanchanawong . National University of Singapore, Singapore

Cadherin-mediated cell adhesions are supramolecular complexes that play essential roles in ligating and mechanically integrating neighboring cells, supporting dynamic coupling between cell-cell adhesions and the contractile actin cytoskeletons. Despite well-documented functions in major aspects of tissue morphogenesis and multicellularity, the ultrastructural organization within cadherin-based adhesions remains unknown, thus obscuring insights into the underlying molecular mechanisms. We mapped the nanoscale organization of key cell-cell junction proteins within cadherin-based adhesions formed on planarized biomimetic cadherin substrate. The enhanced optical accessibility of the planar substrate together with interference-based nanoscopy methods enabled high precision (~10-nm) axial (z) position measurement using common fluorescent proteins. We observed a surprisingly well-organized molecular architecture that stratified along the z-axis, with the cadherin-catenin layer and the actin compartment separated by ~30 nm, interposed by a vinculin-containing interface zone. Our results indicated that vinculin can undergo a conformational activation to span between the cadherin-catenin layer and the actin compartment. The nanoscale positioning of vinculin is determined by alpha-catenin, while vinculin conformational state is controlled by contractility and Abl kinase phosphorylation on the residue Y822 of vinculin. Vinculin activation, in turn, modulates the positioning of VASP and zyxin, inducing VASP-mediated actin polymerization, that likely results in a positive feedback loop that regulates junction strengthening. In conclusion, our measurements reveal a modular nanoscale architecture of cadherin-based adhesions, suggesting a control principle whereby vinculin serves as a molecular clutch that integrates mechanical and biochemical signals to differentially engage the cadherin-catenin complexes to the actomyosin contraction machinery under different contexts such as developmental processes or diseases states.

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