Cartoon of a glutamate synapse containing the major postsynaptic LRRTMs (LRRTM1,2) and neuroligin (NLG1+B) and presynaptic neurexins. β-Neurexins(−S4) bind either LRRTM1,2 or NLG1(+B), β-neurexins(+S4) bind only NLG1(+B), and α-neurexins(−S4) bind only LRRTM1,2. It is not clear whether α-neurexins(+S4) (not shown) are also present; these bind neither LRRTM1,2 nor NLG1(+B). α-Neurexins are necessary to recruit presynaptic calcium channels. LRRTM1,2 and NLG1 bind PSD-95 and related MAGUK scaffolds via different PDZ domains.