ANSTO Nuclear-based science benefitting all Australians
ANSTO Website Search
ANSTO Youtube linkANSTO Facebook LinkANSTO Twitter Link
Research Hub

ANSTO's research capabilities, led by the OPAL nuclear research reactor and associated instruments provide access to users investigating areas as diverse as materials, life sciences, climate change and mining/engineering.

Synaptic arrangement of the Neuroligin/Beta-Neurexin complex revealed by X-ray and Neutron scattering[1]


Davide Comoletti, Igor Tsigelny and Palmer Taylor (UCSD), Alexander Grishaev (NIH), Andrew Whitten and Jill Trewhella (ANSTO)

Autism spectrum disorders have been linked with genetic mutations of the coding regions of the neuroligins and neurexins [2-4].

 

Neuroligins and neurexins are extracellular proteins, essential for forming and maintaining the synaptic connections between nerve cells that enable signals to be transmitted [5]. Many neurodevelopmental disorders involve abnormal synaptic function, but the neuroligins and neurexins are currently the only extracellular synaptic proteins clearly implicated in impaired brain function.

 

Determining the structure of a neuroligin/neurexin complex represents an advance toward defining the molecular organization within the synapse. This structural framework is an essential foundation for linking genetic information with neurodevelopmental disorders. As the neuroligin is heavily glycosylated and possesses unusual extended stalk regions (see below), crystal growth of the extracellular portion of a neuroligin, as well as a neuroligin- neurexin complex, is a challenging endeavor.

 

We therefore turned to small angle X-ray and neutron solution scattering to determine the molecular shapes of neuroligin and neurexin, and their dispositions in their complex, in order to enhance our understanding of the complex formation within the synaptic space environment.

 

Synaptic arrangement figure 1

 

View from the pre-synapatic side ? Green, neuroligin dimer; red, neurexin molecules. Residues found to be mutated in autism are shown as yellow amino acid side chains. N-linked glycosylation sequences are shown in red.

 

Using small-angle X-ray scattering data, a 3-dimensional structural model of the dimeric acetylcholinesterase-like domain for neuroligin-1 was determined. Using this neuroligin-1 model structure, and additional X-ray scattering data and neutron contrast variation data on neuroligin-1 complexed with beta-neurexin, we were able to determine the first three dimensional structural model of this synaptic protein complex (above).

 

These experiments used scattering facilities at SSRL (BL4-2) and NIST (NG3). The combination of X-ray and neutron scattering, sequence analysis, modeling, biochemical and mutagenesis data has allowed us to put forward a model of the neurexin and neuroligin complex in the synaptic space (below). This model provides an important structural framework for linking genetic information on mutated neurexins and neuroligins with neuro-developmental disorders.

 

Synaptic arrangement figure 2

 

The neurexin/neuroligin complex is tethered to the pre- and post-synaptic membranes through their respective O-linked glycosylated regions that have been drawn extended to position the complex in the synaptic space. Arrows specify the approximate sizes of the synaptic cleft and the complex.

 

References

 

  1. Comoletti D, Grishaev A, Whitten AE, Tsigelny I, Taylor P, Trewhella J., Synaptic arrangement of the neuroligin/beta-neurexin complex revealed by X-ray and neutron scattering. Structure 15, 693-705 (2007).
  2. Jamain, S., Quach, H., Betancur, C., Rastam, M., Colineaux, C., Gillberg, I.C., Soderstrom, H., Giros, B., Leboyer, M., Gillberg, C., Bourgeron, T. Paris Autism Research International Sibpair Study. Mutations of the X-linked genes encoding neuroligins NLGN3 and NLGN4 are associated with autism, Nat Genet. 34, 27-29 (2003).
  3. Laumonnier F, Bonnet-Brilhault F, Gomot M, Blanc R, David A, Moizard MP, Raynaud M, Ronce N, Lemonnier E, Calvas P, Laudier B, Chelly J, Fryns JP, Ropers HH, Hamel BC, Andres C, Barthelemy C, Moraine C, Briault S. X-linked mental retardation and autism are associated with a mutation in the NLGN4 gene, a member of the neuroligin family. Am J Hum Genet 74, 552-7 (2004).
  4. Yan, J., Oliveira, G., Coutinho, A., Yang, C., Feng, J., Katz, C., Sram, J., Bockholt, A., Jones, I.R., Craddock, N., Cook, E.H., Vicente, A., Sommer, S.S. (2005) Analysis of the neuroligin 3 and 4 genes in autism and other neuropsychiatric patients, Mol Psychiatry 10, 329-332 (2005).
  5.  Varoqueaux F, Aramuni G, Rawson RL, Mohrmann R, Missler M, Gottmann K, Zhang W, Sudhof TC, Brose N., Neuroligins determine synapse maturation and function. Neuron 51, 741-54 (2006).