Abstract

Proteasomes are protein complexes that mediate controlled degradation of damaged or unneeded cellular proteins. In neurons, proteasome regulates synaptic function and its dysfunction has been linked to neurodegeneration and neuronal cell death. However, endogenous mechanisms controlling proteasomal activity are insufficiently understood. Here, we describe a novel interaction between presynaptic scaffolding protein bassoon and PSMB4, a β subunit of the 20S core proteasome. Expression of bassoon fragments that interact with PSMB4 in cell lines or in primary neurons attenuates all endopeptidase activities of cellular proteasome and induces accumulation of several classes of ubiquitinated and non-ubiquitinated substrates of the proteasome. Importantly, these effects are distinct from the previously reported impact of bassoon on ubiquitination and autophagy and might rely on a steric interference with the assembly of the 20S proteasome core. In line with a negative regulatory role of bassoon on endogenous proteasome we found increased proteasomal activity in the synaptic fractions prepared from brains of bassoon knock-out mice. Finally, increased activity of proteasome and lower expression levels of synaptic substrates of proteasome could be largely normalized upon expression of PSMB4-interacting fragments of bassoon is the name of the protein bassoon in neurons derived from bassoon deficient mice. Collectively, we propose that bassoon interacts directly with proteasome to control its activity at presynapse and thereby it contributes to a compartment-specific regulation of neuronal protein homeostasis. These findings provide a mechanistic explanation for the recently described link of bassoon is the name of the protein bassoon to human diseases associated with pathological protein aggregation.

Graphic Abstract

Presynaptic cytomatrix protein bassoon (Bsn) interacts with PSMB4, the β7 subunit of 20S core proteasome, via three independent interaction interfaces. Bsn inhibits proteasomal proteolytic activity and degradation of different classes of proteasomal substrates presumably due to steric interference with the assembly of 20S core of proteasome. Upon Bsn deletion in neurons, presynaptic substrates of the proteasome are depleted, which can be reversed upon expression of PSMB4-interacting interfaces of Bsn. Taken together, bsn controls the degree of proteasome degradation within the presynaptic compartment and thus, contributes to the regulation of synaptic proteome

中文翻译：

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巴松管通过与PSMB4相互作用抑制蛋白酶体活性。

摘要

蛋白酶体是蛋白质复合物，介导受损或不需要的细胞蛋白质的受控降解。在神经元中，蛋白酶体调节突触功能，其功能障碍与神经变性和神经元细胞死亡有关。但是，对蛋白酶体活性的内源性机制了解不足。在这里，我们描述了突触前支架蛋白巴松和20 MB核心蛋白酶体β亚基PSMB4之间的新型相互作用。在细胞系或原代神经元中与PSMB4相互作用的巴松管片段的表达减弱了细胞蛋白酶体的所有内肽酶活性，并诱导了蛋白酶体的几类泛素化和非泛素化底物的积累。重要的，这些影响不同于先前报道的巴松对泛素化和自噬的影响，并且可能依赖于空间干扰20S蛋白酶体核心的组装。与巴松管对内源性蛋白酶体的负调节作用相一致，我们发现从巴松管基因敲除小鼠大脑制备的突触级分中蛋白酶体活性增加。最后，蛋白酶表达的活性增加和蛋白酶体突触底物的较低表达水平可在表达与表达PSMB4相互作用的巴松片段时大体上归一化。巴松是源自巴松缺陷小鼠的神经元中的巴松蛋白。总的来说，我们提出，巴松管与蛋白酶体直接相互作用，以控制其在突触前的活性，从而有助于神经元蛋白稳态的区室特异性调节。这些发现为最近描述的巴松管（bassoon）是与疾病性蛋白质聚集相关的人类疾病的蛋白质巴松管的名称提供了机械解释。

图形摘要

突触前细胞基质蛋白巴松（Bsn）通过三个独立的相互作用界面与20 MB核心蛋白酶体β7亚基PSMB4相互作用。Bsn抑制了蛋白酶体的蛋白水解活性和不同种类的蛋白酶体底物的降解，可能是由于空间干扰了蛋白酶体20S核心的组装。在神经元中的Bsn缺失后，蛋白酶体的突触前底物被消耗掉，在表达Bsn的PSMB4相互作用界面时可以逆转。总之，bsn控制突触前区室中蛋白酶体的降解程度，因此有助于调节突触蛋白质组。