The broad-spectrum antibiotic D-cycloserine (DCS) is a key component of regimens used to treat multi- and extensively drug-resistant tuberculosis. DCS, a structural analog of D-alanine, binds to and inactivates two essential enzymes involved in peptidoglycan biosynthesis, alanine racemase (Alr) and D-Ala:D-Ala ligase. Inactivation of Alr is thought to proceed via a mechanism-based irreversible route, forming an adduct with the pyridoxal 5'-phosphate cofactor, leading to bacterial death. Inconsistent with this hypothesis, Mycobacterium tuberculosis Alr activity can be detected after exposure to clinically relevant DCS concentrations. To address this paradox, we investigated the chemical mechanism of Alr inhibition by DCS. Inhibition of M. tuberculosis Alr and other Alrs is reversible, mechanistically revealed by a previously unidentified DCS-adduct hydrolysis. Dissociation and subsequent rearrangement to a stable substituted oxime explains Alr reactivation in the cellular milieu. This knowledge provides a novel route for discovery of improved Alr inhibitors against M. tuberculosis and other bacteria.

中文翻译：

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丙氨酸消旋酶对 D-环丝氨酸的破坏和不可逆抑制的限制。

广谱抗生素 D-环丝氨酸 (DCS) 是用于治疗多重和广泛耐药结核病的方案的关键组成部分。DCS 是 D-丙氨酸的一种结构类似物，可结合并灭活参与肽聚糖生物合成的两种必需酶，丙氨酸消旋酶 (Alr) 和 D-Ala:D-Ala 连接酶。Alr 的失活被认为是通过基于机制的不可逆途径进行的，与吡哆醛 5'-磷酸辅因子形成加合物，导致细菌死亡。与该假设不一致的是，在暴露于临床相关的 DCS 浓度后可以检测到结核分枝杆菌 Alr 活性。为了解决这个悖论，我们研究了 DCS 抑制 Alr 的化学机制。对结核分枝杆菌 Alr 和其他 Alrs 的抑制是可逆的，由以前未知的 DCS 加合物水解机制揭示。解离和随后重排成稳定的取代肟解释了细胞环境中的 Alr 再激活。这一知识为发现针对结核分枝杆菌和其他细菌的改进的Alr抑制剂提供了一条新途径。