Proteasomes are highly abundant and conserved protease complexes that eliminate unwanted proteins in the cells. As a single-chain ATP-independent nuclear proteasome activator, proteasome activator 200 (PA200) associates with 20S core particle to form proteasome complex that catalyzes polyubiquitin-independent degradation of acetylated histones, thus playing a pivotal role in DNA repair and spermatogenesis. Here, we present cryo–electron microscopy (cryo-EM) structures of the human PA200-20S complex and PA200 at 2.72 Å and 3.75 Å, respectively. PA200 exhibits a dome-like architecture that caps 20S and uses its C-terminal YYA (Tyr-Tyr-Ala) to induce the α-ring rearrangements and partial opening of the 20S gate. Our structural data also indicate that PA200 has two openings formed by numerous positively charged residues that respectively bind (5,6)-bisdiphosphoinositol tetrakisphosphate (5,6[PP]2-InsP₄) and inositol hexakisphosphate (InsP₆) and are likely to be the gates that lead unfolded proteins through PA200 and into the 20S. Besides, our structural analysis of PA200 found that the bromodomain (BRD)-like (BRDL) domain of PA200 shows considerable sequence variation in comparison to other human BRDs, as it contains only 82 residues because of a short ZA loop, and cannot be classified into any of the eight typical human BRD families. Taken together, the results obtained from this study provide important insights into human PA200-induced 20S gate opening for substrate degradation and the opportunities to explore the mechanism for its recognition of H4 histone in acetylation-mediated proteasomal degradation.

蛋白酶体是高度丰富且保守的蛋白酶复合物，可消除细胞中不需要的蛋白质。作为不依赖单链ATP的核蛋白酶体活化剂，蛋白酶体活化剂200（PA200）与20S核心颗粒结合形成蛋白酶体复合物，该复合物催化乙酰素组蛋白的多泛素非依赖性降解，从而在DNA修复和精子形成中发挥关键作用。在这里，我们介绍人类PA200-20S复合体和PA200分别在2.72Å和3.75Å时的低温电子显微镜（cryo-EM）结构。PA200呈现出一个圆顶状的结构，该结构覆盖20S并使用其C端YYA（Tyr-Tyr-Ala）引起α环重排和20S栅极的部分打开。我们的结构数据还表明，PA200具有两个分别由大量带正电荷的残基形成的开口，这些残基分别结合（5，₄）和六磷酸肌醇（InsP ₆），很可能是导致未折叠蛋白通过PA200进入20S的大门。此外，我们对PA200的结构分析发现，与其他人类BRD相比，PA200的溴结构域（BRD）样（BRDL）结构域显示出相当大的序列变异，因为它的ZA环很短，仅包含82个残基，因此无法分类进入八个典型人类BRD家族中的任何一个。两者合计，从这项研究中获得的结果提供了重要的见解，为人类PA200诱导的20S门打开的底物降解和探索其识别乙酰化介导的蛋白酶体降解中H4组蛋白的机制的机会。