Molecular determinants of cadherin ideal bond formation: Conformation-dependent unbinding on a multidimensional landscape.
Classical cadherin cell-cell adhesion proteins are essential for the formation and maintenance of tissue structures; their primary function is to physically couple neighboring cells and withstand mechanical force. Cadherins from opposing cells bind in two distinct trans conformations: strand-swap dimers and X-dimers. As cadherins convert between these conformations, they form ideal bonds (i.e., adhesive interactions that are insensitive to force). However, the biophysical mechanism for ideal bond formation is unknown. Here, we integrate single-molecule force measurements with coarse-grained and atomistic simulations to resolve the mechanistic basis for cadherin ideal bond formation. Using simulations, we predict the energy landscape for cadherin adhesion, the transition pathways for interconversion between X-dimers and strand-swap dimers, and the cadherin structures that form ideal bonds. Based on these predictions, we engineer cadherin mutants that promote or inhibit ideal bond formation and measure their force-dependent kinetics using single-molecule force-clamp measurements with an atomic force microscope. Our data establish that cadherins adopt an intermediate conformation as they shuttle between X-dimers and strand-swap dimers; pulling on this conformation induces a torsional motion perpendicular to the pulling direction that unbinds the proteins and forms force-independent ideal bonds. Torsional motion is blocked when cadherins associate laterally in a cis orientation, suggesting that ideal bonds may play a role in mechanically regulating cadherin clustering on cell surfaces.
Department of Physics and Astronomy, Iowa State University, Ames, IA 50011; Ames Laboratory, US Department of Energy, Ames, IA 50011;
Kristine
K
Manibog
Bioinformatics and Computational Biology Interdepartmental Program, Iowa State University, Ames, IA 50011; Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, IA 50011;
Kannan
K
Sankar
Department of Physics and Astronomy, Iowa State University, Ames, IA 50011; Ames Laboratory, US Department of Energy, Ames, IA 50011;
Sun-Ae
SA
Kim
Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA 94305;
Yunxiang
Y
Zhang
Department of Physics and Astronomy, Iowa State University, Ames, IA 50011; Bioinformatics and Computational Biology Interdepartmental Program, Iowa State University, Ames, IA 50011; Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, IA 50011; L. H. Baker Center for Bioinformatics and Computational Biology, Iowa State University, Ames, IA 50011.
Robert L
RL
Jernigan
Department of Physics and Astronomy, Iowa State University, Ames, IA 50011; Ames Laboratory, US Department of Energy, Ames, IA 50011; sivasank@iastate.edu.
Sanjeevi
S
Sivasankar
D015820:Cadherins / Q000737:chemistry* / Q000378:metabolism; D056004:Molecular Dynamics Simulation; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D025341:Principal Component Analysis; D011485:Protein Binding; D011487:Protein Conformation; D055503:Protein Multimerization; D013816:Thermodynamics
D015820:Cadherins; D050505:Mutant Proteins
AFM; cell adhesion; mechanobiology; simulations; single-molecule biophysics