Biophysical and Structural Studies of CNTNAP2

At synapses, cell adhesion molecules provide connection between the presynaptic and postsynaptic membranes through homophilic and heterophilic interactions promoting synapse development, function, and plasticity. The synaptic adhesion molecules contactin 2 (CNTN2), and contactin associated protein-like 2 (CNTNAP2) have an emerging role at synaptic interaction networks. CNTNAP2 is a member of the neurexin superfamily of synaptic cell adhesion molecules; it is localized at the juxtaparanodes of myelinated axons at the Nodes of Ranvier where it mediates interactions between neurons and ensheathing glial cells and recruits potassium channels to the juxtaparanodes. CNTNAP2 is also found at synapses. Association, linkage, gene expression and imaging data highlight the role of CNTNAP2 in several neurodevelopment and neuropsychiatric disorders, including developmental language impairment, Morvan’s syndrome, and limbic encephalitis. Cell biology and immunological studies strongly indicate that CNTNAP2 binds to CNTN2. CNTNAP2 and CNTN2 form a macromolecular complex spanning axo-glial and synaptic contacts to maintain neuron-neuron and axo-glial interactions. Currently, it is not known how CNTNAP2 and CNTN2 interact, nor whether CNTNAP2 binds additional cell surface molecules. High-resolution information on the three dimensional atomic structure of CNTNAP2 is also not known.
The goal during of this master’s thesis project was to purify the extracellular domain of CNTNAP2 and several of its fragments, assess whether the extracellular domains of CNTNAP2 and CNTN2 interact directly using solid phase binding assays and obtain crystals of CNTNAP2 fragments. We are the first who did in vitro studies for characterize CNTNAP2 and their partner CNTN2. We found that CNTNAP2 is an endogenous ligand for CNTN2 and associates with nanomolar affinity. The binding of the extracellular domains of CNTNAP2 and CNTN2 are promoted by the presence of Ca2+. These data provide new platform for structural-functional study for CNTNAP2/CNTN2 complex. In the future, we will continue this project to map critical interactions sites on these proteins.