Cryo-EM structures of the full-length human contactin-2

Area of Science:

• Neuroscience
• Structural Biology
• Cell Biology

Background:

• Contactin-2 (CNTN2), an immunoglobulin cell adhesion molecule (IgCAM), plays vital roles in neural development, including myelination, neural communication, and cell migration.
• The precise assembly and structural mechanisms underlying full-length CNTN2 function, particularly its role in cell adhesion, remain incompletely understood.

Purpose of the Study:

• To elucidate the structural basis of full-length human CNTN2 assembly and its role in cell adhesion.
• To investigate the functional significance of CNTN2 homodimerization and specific domain interactions.

Main Methods:

• Determined the cryo-electron microscopy (cryo-EM) structures of full-length human CNTN2.
• Utilized structure-guided mutagenesis analyses to assess the role of homodimerization and specific domains in cell adhesion.
• Investigated concentration-dependent homodimer formation in vitro.

Main Results:

• Full-length human CNTN2 forms a concentration-dependent homodimer.
• The cryo-EM structure reveals a novel bowknot-shaped scaffold formed by the Ig1-6 repeats of two protomers, with outward-extending FNIII repeats.
• The Ig1-6 domains, not previously recognized Ig1-4 domains, are essential for CNTN2-mediated cell adhesion and clustering, with homodimerization being critical for this function.

Conclusions:

• The Ig1-6 domains and homodimerization are indispensable for CNTN2's role in cell adhesion within the nervous system.
• The study provides novel structural insights into how CNTN2 forms homodimers to establish and maintain neural cell-cell contacts.