人组蛋白脱乙酰酶 4 (HDAC4) 属于锌依赖性组蛋白脱乙酰酶 IIa 类。 HDAC4 是多种适应症领域的既定靶标，特别是亨廷顿病、心力衰竭和癌症。为了减少不需要的副作用，开发同工酶选择性抑制剂是有利的，但由于 HDAC 家族高度保守的活性中心，这构成了重大挑战。根据目前的知识，假设 HDAC4wt 中的 H976 只出现在外构象中，因此选择性脚袋是组成性开放的。相比之下，HDAC4H976Y中相应酪氨酸的侧链采用不合构象，因此能够稳定脱乙酰反应的中间状态并阻断进入足袋。在这项研究中，我们提供的证据表明 HDAC4wt 的内构象和外构象之间存在动态平衡。解决足袋问题的选择性 HDAC4 抑制剂的结合可以在主要具有小侧链但也具有中等疏水性或极性侧链的 HDAC4 变体中得到增强。我们将此归因于这些侧链优先存在于外构象中的事实。因此，我们建议 HDAC4H976A 和其他 HDAC4 变体作为有前途的工具，用于在筛选活动中寻找和丰富 HDAC4 选择性脚袋粘合剂，这些粘合剂在 HDAC4wt 的传统筛选中可能被忽视。版权所有 © 2024 作者。由爱思唯尔公司出版。保留所有权利。

Human histone deacetylase 4 (HDAC4) belongs to class IIa of the zinc-dependent histone deacetylases. HDAC4 is an established target for various indication areas, in particular Huntington's disease, heart failure and cancer. To reduce unwanted side effects, it is advantageous to develop isozyme-selective inhibitors, which poses a major challenge due to the highly conserved active centers of the HDAC family. According to current knowledge it is assumed that H976 in HDAC4wt occurs exclusively in the out-conformation and thus the selective foot pocket is constitutively open. In contrast, the side chain of the corresponding tyrosine in HDAC4H976Y adopts the in-conformation, and is thus able to stabilize the intermediate state of the deacetylation reaction and block access to the foot pocket. In this study, we provide evidence that a dynamic equilibrium exists between the in- and out-conformation in HDAC4wt. The binding of selective HDAC4 inhibitors that address the foot pocket can be enhanced in HDAC4 variants with mainly small, but also medium hydrophobic or polar side chains. We attribute this to the fact that these side chains are preferentially present in the out-conformation. Therefore, we propose HDAC4H976A and other HDAC4 variants as promising tools to find and enrich HDAC4-selective foot pocket binders in screening campaigns that might have been overlooked in conventional screens with HDAC4wt.Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.