Structure
In mammals, neurexin is encoded by three different genes (NRXN1, 2, and 3) each controlled by two different promoters (an upstream α and a downstream β promoter) resulting in α-neurexins 1-3 and β-neurexins 1-3. In addition, there are alternative splicing at 5 sites in α-neurexin and 2 in β-neurexin, more than 2000 splice variants are possible, suggesting its role in determining synapse specificity.
The encoded proteins are structurally similar to laminin, slit, and agrin, other proteins involved in axon guidance and synaptogenesis. α-Neurexins and β-neurexins have identical intracellular domains but different extracellular domains. The extracellular domain of α-neurexin is composed of three neurexin repeats which each contain LNS (laminin, nectin, sex-hormone binding globulin) – EGF (epidermal growth factor) – LNS domains. N1α binds to a variety of ligands including neuroligins and GABA receptors, though neurons of every receptor type express neurexins. β-Neurexins are shorter versions of α-neurexins, containing only one LNS domain. β-Neurexins (located presynaptically) act as receptors for neuroligin (located postsynaptically). Additionally, β-Neurexin has also been found to play a role in angiogenesis.
The C terminus of the short intracellular section of both types of neurexins binds to synaptotagmin and to the PDZ (postsynaptic density (PSD)-95/discs large/zona-occludens-1) domains of CASK and Mint. These interactions form connections between intracellular synaptic vesicles and fusion proteins. Thus neurexins play an important role in assembling presynaptic and postsynaptic machinery.
Trans-synapse, the extracellular LNS domains have a functional region, the hyper-variable surface, formed by loops carrying 3 splice inserts. This region surrounds a coordinated Ca2+ ion and is the site of neuroligin binding, resulting in a neurexin-neuroligin Ca2+-dependent complex at the junction of chemical synapses.
Read more about this topic: Neurexin
Famous quotes containing the word structure:
“The philosopher believes that the value of his philosophy lies in its totality, in its structure: posterity discovers it in the stones with which he built and with which other structures are subsequently built that are frequently better—and so, in the fact that that structure can be demolished and yet still possess value as material.”
—Friedrich Nietzsche (1844–1900)
“Vashtar: So it’s finished. A structure to house one man and the greatest treasure of all time.
Senta: And a structure that will last for all time.
Vashtar: Only history will tell that.
Senta: Sire, will he not be remembered?
Vashtar: Yes, he’ll be remembered. The pyramid’ll keep his memory alive. In that he built better than he knew.”
—William Faulkner (1897–1962)
“Agnosticism is a perfectly respectable and tenable philosophical position; it is not dogmatic and makes no pronouncements about the ultimate truths of the universe. It remains open to evidence and persuasion; lacking faith, it nevertheless does not deride faith. Atheism, on the other hand, is as unyielding and dogmatic about religious belief as true believers are about heathens. It tries to use reason to demolish a structure that is not built upon reason.”
—Sydney J. Harris (1917–1986)