This overlap is easily explained by the fact that Cav2 channels are physically and functionally tightly associated with exocytotic sites. Not surprisingly, the Cav2 proteome also contains many PSD proteins since in that study no separation of pre- and postsynaptic compartments was attempted. Considering the high purity of our docked synaptic vesicle fraction, with proteins from other organelles (except mitochondria) being virtually absent, the identification of 30 hitherto uncharacterized proteins suggests that many of them are indeed constituents of the presynaptic active zone and adjacent

areas. While further work will be needed to clarify which of them is involved in presynaptic function, we have used in silico-based analyses for a preliminary characterization (Table S4). Accordingly, 16 proteins possess one or more predicted transmembrane domains. Twenty-six proteins appear to be conserved Obeticholic Acid between vertebrates, among these 12 are also conserved in invertebrates. Noteworthy, 18 proteins appear to be well expressed

in the mammalian brain based on standardized in situ hybridization (Allen Mouse Brain Atlas, http://mouse.brain-map.org). Thus, we consider it highly probable that at least some of these proteins will turn out to be constituents of the presynaptic membrane and/or the vesicular release apparatus. We extended our study to investigate the differences between glutamatergic versus GABAergic docking complexes by a slight modification of our original protocol. We Selleck LGK 974 find that, except of the transmitter-specific transporters and enzymes, only very few proteins are selectively enriched in glutamatergic and GABAergic docking complexes. These results confirm and extend our previous observation that glutamatergic and oxyclozanide GABAergic synaptic vesicles have

a largely identical protein composition. Two major conclusions can be drawn from these findings. First, the release machineries of glutamatergic and GABAergic synapses are very similar if not identical. In particular, we did not detect any major difference between the expression levels of SNAP25 and SNAP23 in the two types of synapses, arguing against a specialization of these SNAREs for glutamatergic versus GABAergic release as suggested previously (Garbelli et al., 2008; Verderio et al., 2004). Obviously, the overall similarity between the populations does not exclude major variations in the composition of the docking and release apparatus between individual synapses. However, such variations do not appear to correlate with the neurotransmitter phenotype. Second, it is only the biosynthetic enzymes and the transmitter transporters (particularly the vesicular transporters) that define the neurotransmitter phenotype of glutamatergic and GABAergic synapses. Taken together, we have made significant progress toward the aim of establishing a “parts list” of the presynaptic docking and release machinery and of the presynaptic membrane.