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Single-Cell Biophysics: Measurement, Modulation, and Modeling
Saturday Speaker Abstracts
13
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.