Structural insights into modulation and selectivity of transsynaptic neurexin-LRRTM interaction

Area of Science:

• Neuroscience
• Structural Biology
• Molecular Biology

Background:

• Leucine-rich repeat transmembrane neuronal proteins (LRRTMs) are crucial for excitatory synapse organization.
• Neurexins (Nrxns) and heparan sulfate proteoglycans are identified presynaptic ligands for LRRTMs.
• LRRTM1 and LRRTM2 specifically bind Nrxn splice variants lacking the S4 insertion.

Purpose of the Study:

• To determine the crystal structure of the Neurexin 1 beta (Nrxn1β)-LRRTM2 complex.
• To elucidate the molecular mechanism underlying the selective binding between Nrxns and LRRTM1/2.
• To investigate the role of the Nrxn S4 splice insertion in modulating this interaction.

Main Methods:

• X-ray crystallography to obtain the 3.4 Å resolution structure of the Nrxn1β-LRRTM2 complex.
• Structure-based mutational analyses at both molecular and cellular levels.

Main Results:

• The crystal structure reveals the Nrxn1β-LRRTM2 interface, highlighting Ca²⁺-mediated interactions.
• This interface overlaps with the known Neurexin-neuroligin binding site.
• Mutational analyses confirm the mechanism of selective Nrxn-LRRTM binding and the modulatory effect of the Nrxn S4 insertion.

Conclusions:

• The structural and functional data provide a detailed understanding of the selective Nrxn-LRRTM interaction.
• This interaction is critical for excitatory synapse development and function.
• The S4 splice site in Nrxns plays a key role in regulating synaptic connections.