Cadherin Extracellular Domain Clustering in the Absence of Trans-Interactions

While both cis and trans (adhesive)-interactions cooperate in the assembly of intercellular adhesions, computational simulations have predicted that two-dimensional confinement may promote cis -oligomerization, in the absence of trans -interactions. Here, single-molecule tracking of cadherin extracellular domains on supported lipid bilayers revealed the density-dependent formation of oligomers and cis -clusters in the absence of trans -interactions. Lateral oligomers were virtually eliminated by mutating a putative cis (lateral) binding interface. At low cadherin surface coverage, wild-type and mutant cadherin diffused rapidly, consistent with the motion of a lipid molecule within a cadherin-free supported bilayer and with cadherins diffusing as monomers. Although the diffusion of mutant cadherin did not change appreciably with increasing surface coverage, the average short-time diffusion coefficient of wild-type cadherin slowed significantly above a fractional surface coverage of ∼0.01 (∼1100 molecules/μm 2 ). A detailed analysis of molecular trajectories suggested the presence of a broad size distribution of cis -cadherin oligomers. These findings verify predictions that two-dimensional confinement promotes cis -oligomerization, in the absence of trans -interactions.