Tubulin and GTP Are Crucial Elements for Postsynaptic Density Construction and Aggregation

In our previous experiments on the postsynaptic density lattice (PSDL), which is thought to serve as the backbone structure for the PSD, we suggested that tubulin plays a fundamental role in the PSD structure at excitatory synapses. In this study, we further reveal an unrecognized characteristic of tubulin within the PSD. First, using electron microscopy, we identified an interaction between postsynaptic structures (PSDL and PSD) and polymerizing microtubules, which led to the binding of polymerizing microtubules to PSDL and PSD. In turn, this interaction induced changes in the microtubule morphology. These results support earlier findings suggesting that microtubules transiently intruding into the spine head can associate with PSDs, inducing structural changes in the PSD. Next, we observed that the structural integrity of both PSD and PSDL was compromised upon exposure to GTP and microtubule-affecting reagents. These findings reinforce the idea that tubulin is a crucial building block of the PSD architecture. Moreover, we found that PSD aggregation was enhanced following interactions with polymerizing tubulin and was disintegrated upon treatment with GTP and microtubule-affecting reagents. These results indicate that microtubules also play a key role in PSD aggregation in vitro. Collectively, our study highlights the involvement of tubulin in the construction, function (specifically its interaction with polymerizing microtubules), and aggregation of the PSD, which may impact both physiological and pathological conditions. Furthermore, our in vitro findings suggest that GTP can either destroy or induce the enlargement and reorganization of PSD structures, depending on its interaction with growing microtubules.