The stringent response, controlled by (p)ppGpp, enables bacteria to trigger a strong phenotypic resetting that is crucial to cope with adverse environmental changes and is required for stress survival and virulence. In the bacterial cell, (p)ppGpp levels are regulated by the concerted opposing activities of RSH (RelA/SpoT homologue) enzymes that can transfer a pyrophosphate group of ATP to the 3′ position of GDP (or GTP) or remove the 3′ pyrophosphate moiety from (p)ppGpp. Bifunctional Rel enzymes are notoriously difficult to crystallize owing to poor stability and a propensity for aggregation, usually leading to a loss of biological activity after purification. Here, the production, biochemical analysis and crystallization of the bifunctional catalytic region of the Rel stringent factor from Thermus thermophilus (Rel_Tt^NTD) in the resting state and bound to nucleotides are described. Rel_Tt and Rel_Tt^NTD are monomers in solution that are stabilized by the binding of Mn²⁺ and mellitic acid. Rel_Tt^NTD crystallizes in space group P4₁22, with unit‐cell parameters a = b = 88.4, c = 182.7 Å, at 4°C and in space group P4₁2₁2, with unit‐cell parameters a = b = 105.7, c = 241.4 Å, at 20°C.

中文翻译：

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嗜热栖热菌的相对严格因子：结晶和 X 射线分析。

由 (p)ppGpp 控制的严格反应使细菌能够触发强烈的表型重置，这对于应对不利的环境变化至关重要，并且是应激生存和毒力所必需的。在细菌细胞中，(p)ppGpp 水平受 RSH（RelA/SpoT 同源物）酶的协同反向活性调节，这些酶可将 ATP 的焦磷酸基团转移到 GDP（或 GTP）的 3' 位置或去除 3' 位置(p)ppGpp 的焦磷酸部分。双功能 Rel 酶由于稳定性差和聚集倾向而难以结晶，通常导致纯化后生物活性丧失。在此，描述了来自嗜热栖热菌的 Rel 严格因子(Rel _Tt ^NTD ) 在静息状态下并与核苷酸结合的双功能催化区的生产、生化分析和结晶。Rel _Tt和 Rel _Tt ^{NTD是溶液中的单体，通过 Mn 2+}和苯六甲酸的结合而稳定。Rel _Tt ^NTD在空间群P 4 ₁ 22 中结晶，晶胞参数a = b = 88.4，c = 182.7 Å，温度为 4°C，在空间群P 4 ₁ 2 ₁ 2 中，晶胞参数a = b = 105.7，c = 241.4 埃，20°C 时。