Molecular mechanism underlying RAG1/RAG2 synaptic complex formation.

Area of Science:

• Molecular Biology
• Immunology
• Biophysics

Background:

• The RAG1 and RAG2 (RAG) proteins are essential for V(D)J recombination, a process critical for adaptive immunity.
• Understanding the structure of RAG synaptic complexes is vital for comprehending V(D)J recombination, but remains poorly defined.

Purpose of the Study:

• To visualize and characterize the structure of RAG synaptic complexes using atomic force microscopy.
• To determine RAG protein stoichiometry and DNA arrangement within the synaptosome.

Main Methods:

• Atomic force microscopy (AFM) was employed to directly visualize RAG synaptic complexes.
• Mass calculations and analysis of DNA configuration were performed on visualized complexes.

Main Results:

• Pre-cleavage RAG synaptic complexes exhibit approximately double the protein content of single RAG-RSS complexes, consistent with a pair of RAG heterotetramers.
• Recombination signal sequences (RSSs) in the synaptic complex are primarily arranged side-by-side, without DNA strand crossover.
• An association model for complex assembly, involving RAG protein-protein interactions, is favored.
• Cation composition (Mg2+ vs. Ca2+) significantly alters RAG-RSS complex stoichiometry.

Conclusions:

• Direct visualization reveals the structural basis of RAG synaptic complex formation.
• The findings support an association model for RAG complex assembly and highlight the role of cations in regulating complex formation.
• This structural information provides critical insights into the mechanism of V(D)J recombination.