-cysteine, a primary building block of mycothiol, plays an essential role in the defense mechanism of (). However, it is unclear how regulates cysteine biosynthesis as no study has reported the cysteine regulatory complex (CRC) in . Serine acetyltransferase (SAT) and cysteine synthase (CS) interact to form CRC. Although CS has been characterized well, minimal information is available on SAT, which synthesizes, O-acetylserine (OAS), the precursor of cysteine. This study fills the gap and provides experimental evidence for the presence of CRC and a non-canonical multi-oligomeric SAT. We employed multiple analytical methods to characterize the oligomeric and kinetic properties of SAT and CRC. Results show that SAT, lacking >75 N-terminal amino acids exists in three different assembly states; trimer, hexamer, and dodecamer, compared to the single hexameric state of SAT of other bacteria. While hexamers display the highest catalytic turnover, the trimer is the least active. The predominance of trimers at low physiologically relevant concentrations suggests that SAT displays the lowest catalytic potential known. Further, the catalytic potential of SAT is also significantly reduced in CRC state, in contrast to enhanced activity of SAT in CRC of other organisms. Our study provides insights into multi-oligomeric SAT with reduced catalytic potential and demonstrates that both SAT and CS of interact to form CRC, although with altered catalytic properties. We discuss our results in light of the altered biochemistry of the last step of canonical sulfate-dependent cysteine biosynthesis of .

中文翻译：

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结核分枝杆菌的多寡聚和催化受损的丝氨酸乙酰转移酶和半胱氨酸调节复合物

-半胱氨酸是菌硫醇的主要组成部分，在 () 的防御机制中发挥着重要作用。然而，目前尚不清楚如何调节半胱氨酸生物合成，因为没有研究报道半胱氨酸调节复合物（CRC）。丝氨酸乙酰转移酶 (SAT) 和半胱氨酸合酶 (CS) 相互作用形成 CRC。尽管 CS 已得到很好的表征，但有关 SAT 的信息却很少，它合成 O-乙酰丝氨酸 (OAS)，即半胱氨酸的前体。这项研究填补了空白，并为 CRC 和非规范多寡聚 SAT 的存在提供了实验证据。我们采用多种分析方法来表征 SAT 和 CRC 的低聚物和动力学特性。结果表明，缺少 >75 个 N 端氨基酸的 SAT 存在三种不同的组装状态；与其他细菌的 SAT 单一六聚体状态相比，三聚体、六聚体和十二聚体。虽然六聚体显示出最高的催化转化率，但三聚体的活性最低。三聚体在低生理相关浓度下的优势表明 SAT 显示出已知的最低催化潜力。此外，与其他生物体 CRC 中 SAT 的活性增强相比，SAT 的催化潜力在 CRC 状态下也显着降低。我们的研究提供了对催化潜力降低的多寡聚 SAT 的见解，并表明 SAT 和 CS 相互作用形成 CRC，尽管催化性能发生了改变。我们根据经典硫酸盐依赖性半胱氨酸生物合成最后一步的生物化学改变来讨论我们的结果。