The ubiquitin-specific protease (USP) family of deubiquitinases (DUBs) controls cellular ubiquitin-dependent signaling events. This generates therapeutic potential, with active-site inhibitors in preclinical and clinical studies. Understanding of the USP active site is primarily guided by USP7 data, where the catalytic triad consists of cysteine, histidine, and a third residue (third critical residue), which polarizes the histidine through a hydrogen bond. A conserved aspartate (fourth critical residue) is directly adjacent to this third critical residue. Although both critical residues accommodate catalysis in USP2, these residues have not been comprehensively investigated in other USPs. Here, we quantitatively investigate their roles in five USPs. Although USP7 relies on the third critical residue for catalysis, this residue is dispensable in USP1, USP15, USP40, and USP48, where the fourth critical residue is vital instead. Furthermore, these residues vary in importance for nucleophilic attack. The diverging catalytic mechanisms of USP1 and USP7 are independent of substrate and retained in cells for USP1. This unexpected variety of catalytic mechanisms in this well-conserved protein family may generate opportunities for selective targeting of individual USPs.

中文翻译：

---

USP 去泛素酶催化机制的多样性。

去泛素酶 (DUB) 的泛素特异性蛋白酶 (USP) 家族控制细胞泛素依赖性信号传导事件。这在临床前和临床研究中利用活性位点抑制剂产生了治疗潜力。对 USP 活性位点的理解主要以 USP7 数据为指导，其中催化三联体由半胱氨酸、组氨酸和第三个残基（第三个关键残基）组成，第三个残基通过氢键极化组氨酸。保守的天冬氨酸（第四个关键残基）与该第三个关键残基直接相邻。尽管这两种关键残留物在 USP2 中都具有催化作用，但这些残留物尚未在其他 USP 中得到全面研究。在这里，我们定量研究了它们在五个 USP 中的作用。虽然USP7依赖第三个关键残基进行催化，但该残基在USP1、USP15、USP40和USP48中是可有可无的，而第四个关键残基却至关重要。此外，这些残基对于亲核攻击的重要性各不相同。 USP1 和 USP7 的不同催化机制独立于底物并保留在 USP1 的细胞中。这个保守的蛋白质家族中这种意想不到的多种催化机制可能会为选择性靶向单个 USP 带来机会。