A double S shape provides the structural basis for the extraordinary binding specificity of Dscam isoforms

Area of Science:

• Neuroscience
• Molecular Biology
• Genetics

Background:

• Drosophila Dscam proteins generate extensive isoform diversity.
• This diversity is critical for accurate neural circuit formation.
• Isoforms exhibit specific homophilic binding, crucial for cell recognition.

Purpose of the Study:

• To elucidate the structural basis of Dscam isoform-specific homophilic binding.
• To understand the molecular mechanisms underlying cell recognition in the Drosophila brain.

Main Methods:

• X-ray crystallography to determine the structure of Dscam(1-8).
• Genetic and biochemical assays to validate binding interactions.

Main Results:

• The structure of Dscam(1-8) reveals a symmetric homodimer with an S-shaped conformation.
• This structure facilitates antiparallel 'matching' of variable immunoglobulin domains.
• Intramolecular interactions between constant domains also contribute to homophilic binding.

Conclusions:

• Dscam homophilic binding specificity arises from the 'matching' of three variable Ig domains.
• Intramolecular interactions stabilize the homodimer and contribute to binding specificity.
• These findings provide a structural framework for understanding Dscam-mediated cell recognition.