Cadherin mechanics and complexation: the importance of calcium binding.
E-cadherins belong to a family of membrane-bound, cellular adhesion proteins. Their adhesive properties mainly involve the two N-terminal extracellular domains (EC1 and EC2). The junctions between these domains are characterized by calcium ion binding sites, and calcium ions are essential for the correct functioning of E-cadherins. Calcium is believed to rigidify the extracellular portion of the protein, which, when complexed, adopts a rod-like conformation. Here, we use molecular dynamics simulations to investigate the dynamics of the EC1-2 portion of E-cadherin in the presence and in the absence of calcium ions. These simulations confirm that apo-cadherin shows much higher conformational flexibility on a nanosecond timescale than the calcium-bound form. It is also shown that although the apo-cadherin fragment can spontaneously complex potassium, these monovalent ions are incapable of rigidifying the interdomain junctions. In contrast, removal of the most solvent-exposed calcium ion at the EC1-2 junction does not significantly perturb the dynamical behavior of the fragment. We have also extended this study to the cis-dimer formed from two EC1-2 fragments, potentially involved in cellular adhesion. Here again, it is shown that the presence of calcium is an important factor in both rigidifying and stabilizing the complex.
Cailliez
Fabien
F
Laboratoire de Biochimie Théorique, CNRS, UPR 9080, Institut de Biologie Physico-Chimique, Paris 75005, France.
Lavery
Richard
R
D001665:Binding Sites; D015820:Cadherins / Q000737:chemistry*; D002118:Calcium / Q000737:chemistry*; D003198:Computer Simulation; D007700:Kinetics; D019563:Mechanics; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D009038:Motion; D011485:Protein Binding; D017434:Protein Structure, Tertiary
D015820:Cadherins; D002118:Calcium