Crystallization and low-resolution structure solution of the SALM3-PTPσ synaptic adhesion complex.

Synaptic adhesion molecules are major organizers of the neuronal network and play a crucial role in the regulation of synapse development and maintenance in the brain. Synaptic adhesion-like molecules (SALMs) and leukocyte common antigen-related receptor protein tyrosine phosphatases (LAR-PTPs) are adhesion protein families with established synaptic function. Dysfunction of several synaptic adhesion molecules has been linked to cognitive disorders such as autism spectrum disorders and schizophrenia. A recent study of the binding and complex structure of SALM3 and PTPσ using small-angle X-ray scattering revealed a 2:2 complex similar to that observed for the interaction of human SALM5 and PTPδ. However, the molecular structure of the SALM3-PTPσ complex remains to be determined beyond the small-angle X-ray scattering model. Here, the expression, purification, crystallization and initial 6.5 Å resolution structure of the mouse SALM3-PTPσ complex are reported, which further verifies the formation of a 2:2 trans-heterotetrameric complex similar to the crystal structure of human SALM5-PTPδ and validates the architecture of the previously reported small-angle scattering-based solution structure of the SALM3-PTPσ complex. Details of the protein expression and purification, crystal optimization trials, and the initial structure solution and data analysis are provided.