Biology subjects

Kaizuka, T.

Publications and source records attributed to Kaizuka, T..

3 recordsLinked to original sources

bioRxiv2024

3D super-resolution imaging of PSD95 reveals an abundance of diffuse protein supercomplexes in the mouse brain

PSD95 is an abundant scaffolding protein that assembles multiprotein complexes controlling synaptic physiology and behavior. Confocal microscopy has previously shown that PSD95 is enriched in the postsynaptic terminals of excitatory synapses and 2D super-resolution microscopy further revealed that it forms nanoclusters. In this study, we utilized 3D super-resolution microscopy to examine the nanoarchitecture of PSD95 in the mouse brain, characterizing over 8 million molecules. While we were able to identify structural subtypes previously reported, imaging in 3D allowed us to classify these with higher accuracy. Furthermore, 3D super-resolution microscopy enabled the quantification of protein levels, revealing an abundance of PSD95 molecules existed outside of synapses as a diffuse population of supercomplexes, containing multiple copies of PSD95. Further analysis of the supercomplexes containing two units identified two populations: one that had PSD95 molecules separated by 39 {+/-} 2 nm, and a second with a separation of 94 {+/-} 27 nm. These results suggest that PSD95 supercomplexes containing multiple protein copies assemble outside the synapse and then integrate into the synapse to form a supramolecular nanocluster architecture.

biophysics↗

bioRxiv2023

The organisation and turnover of synaptic proteins within molecular supercomplexes.

The concept that dimeric protein complexes in synapses can sequentially replace their subunits has been a cornerstone of Francis Cricks 1984 hypothesis, explaining how long-term memories could be maintained in the face of short protein lifetimes. However, it is unknown whether the subunits of protein complexes that mediate memory are sequentially replaced in the brain and if this process is linked to protein lifetime. We address these issues by focusing on supercomplexes assembled by the abundant postsynaptic scaffolding protein PSD95, which plays a crucial role in memory. We used single-molecule detection, super-resolution microscopy and MINFLUX to probe the molecular composition of PSD95 supercomplexes in mice carrying genetically encoded HaloTags, eGFP and mEos2. We found a population of PSD95-containing supercomplexes comprised of two copies of PSD95, with a dominant 12.7 nm separation. Time-stamping of PSD95 subunits in vivo revealed that each PSD95 subunit was sequentially replaced over days and weeks. Comparison of brain regions showed subunit replacement was slowest in the cortex, where PSD95 protein lifetime is longest. Our findings reveal that protein supercomplexes within the postsynaptic density can be maintained by gradual replacement of individual subunits providing a mechanism for stable maintenance of their organization. Moreover, we extend Cricks model by suggesting that synapses with slow subunit replacement of protein supercomplexes and long protein lifetimes are specialized for long-term memory storage and that these synapses are highly enriched in superficial layers of the cortex where long-term memories are stored.

neuroscience↗

bioRxiv2023

DRACC1, a major postsynaptic protein, regulates the condensation of postsynaptic proteins via liquid-liquid phase separation

Numerous proteome analyses have been conducted on the postsynaptic density (PSD), a protein condensate beneath the postsynaptic membrane of excitatory synapses. Each has identified several hundred to thousands of proteins. While proteins with predictable functions have been well studied, functionally uncharacterized proteins are mostly overlooked. In this study, we perform a meta-analysis of the 35 PSD proteome datasets, including 5,869 proteins, identifying 97 uncharacterized proteins that appeared in multiple datasets. We focus on the top-ranked protein, FAM81A, renamed DRACC1. DRACC1 is expressed in forebrain neurons and enriched at the synapse. DRACC1 interacts with PSD proteins, including PSD-95, SynGAP, and NMDA receptors, and promotes liquid-liquid phase separation of those proteins. Consistently, the downregulation of DRACC1 in neurons causes a decrease in the size of PSD-95 puncta and the frequency of neuronal firing. Our results characterize DRACC1 as a novel synaptic protein facilitating the assembly of proteins within PSD. It also indicates the effectiveness of a meta-analytic approach of existing proteome datasets in identifying uncharacterized proteins.

neuroscience↗