A lipid closes a loop

PLoS Biol. 12, e1001908 (2014)

Credit: PLOS BIOLOGY

GABAergic synapses, characterized by the presence of GABA_A receptors (GABA_ARs), are involved in inhibition of neuronal signals. Gephyrin is a scaffold protein that regulates the clustering of, and therefore the number of, GABA_ARs at synapses, which is important for functional plasticity. A recent proteomic study showed that gephyrin may be palmitoylated at inhibitory synapses. To learn more about how gephyrin is regulated, Dejanovic et al. used fractionation experiments, metabolic labeling in conjunction with biochemistry as well as small-molecule inhibition of palmitoyl transferases (so-called DHHC enzymes) to confirm that gephyrin is palmitoylated in vivo. Mutation of various gephyrin residues combined with MS identified the palmitoylated residues as Cys212 and Cys284. Mutation of both amino acids abolished gephyrin palmitoylation and the postsynaptic clustering mediated by gephyrin. Complementary screens in HEK cells and in primary neurons followed by the use of dominant-negative DHHC-12, its overexpression and its knockdown identified this palmitoyltransferase as the main gephyrin-palmitoylating enzyme. DHHC-12 expression in primary hippocampal neurons increased the size of postsynaptic gephyrin clusters and increased the amplitude of miniature postsynaptic currents, indicative of an increase in the GABA_AR pool, whereas a GABA_AR antagonist inhibited gephyrin palmitoylation. These results suggest that GABA_AR-mediated increases in gephyrin palmitoylation promote postsynaptic clustering of the receptor itself.