Figure 5.

Definition of single residues essential for neurexin synaptogenic activity. A–D, Although the D157A mutation (A) showed strong induction of gephyrin and PSD-95 clusters, other mutations such as T156A (B) caused moderate reduction of PSD-95 clustering only. Other mutations such as D158A (C) caused more severe reductions in both gephyrin and PSD-95 clustering, whereas the R109A (D) mutation completely abolished gephyrin and PSD-95 clustering. Arrowheads indicate synapsin-negative induced clusters, whereas arrows indicate endogenous clusters that are synapsin positive. E, The effect of each mutation on synaptogenic activity was determined by quantifying the percentage of transfected fibroblasts overlaying dendrites that induced gephyrin or PSD-95 clustering. For gephyrin: +++, 80–100%; ++, 40–79%; +, 1–39%; −, 0%. For PSD-95: +++, 60–80%; ++, 25–59%; +, 1–24%; −, 0%. Position refers to the location of the mutation or its function as a predicted Ca²⁺-binding residue. F, The model shows the location of residues that abolished induction of both gephyrin and PSD-95 clustering (red), reduced both gephyrin and PSD-95 clustering (blue), reduced PSD-95 but not gephyrin clustering (green), or had no effect on neurexin synaptogenic activity (purple). Scale bar, 10 μm.