AbstractSanglifehrin A (SFA) is a spirolactam‐conjugated, 22‐membered macrolide with remarkable immunosuppressive and antiviral activities. This macrolide is a result of a hybrid polyketide synthase (PKS)‐nonribosomal peptide synthetase (NRPS) assembly line that utilizes (2S)‐2‐ethylmalonamyl as a starter unit. Here, we report that the formation and loading of this starter unit in the SFA assembly line involve two unusual enzymatic reactions that occur on a discrete acyl carrier protein (ACP), SfaO. An amide synthetase, SfaP, catalyzes the amidation of (2S)‐2‐ethylmalonyl in a SfaO‐dependent manner. Then, a β‐ketoacyl‐ACP synthase III‐like protein, SfaN, transfers resultant (2S)‐2‐ethylmalonamyl from SfaO onto the loading ACP domain of the hybrid PKS‐NRPS assembly line to prime SFA biosynthesis. Both SfaP and SfaN display promiscuous activities. This study furthers the appreciation of assembly line chemistry, as a new paradigm for unusual building block formation and incorporation is provided.
摘要长寿素 A(SFA)是一种螺内酰胺共轭的 22 元大环内酯,具有显著的免疫抑制和抗病毒活性。这种大环内酯是多酮肽合成酶(PKS)-非核糖体肽合成酶(NRPS)混合装配线的产物,利用 (2S)-2- 乙基丙二酰基作为起始单元。在这里,我们报告了这种起始单元在 SFA 组装线中的形成和装载涉及两个不同寻常的酶促反应,它们发生在一个离散的酰基载体蛋白(ACP)SfaO 上。酰胺合成酶 SfaP 以依赖 SfaO 的方式催化 (2S)-2-ethylmalonyl 的酰胺化反应。然后,β-酮酰-ACP 合酶 III 样蛋白 SfaN 将 SfaO 产生的 (2S)-2-ethylmalonamyl 转移到混合 PKS-NRPS 组装线的负载 ACP 结构域上,为 SFA 的生物合成提供能量。SfaP 和 SfaN 都具有杂交活性。这项研究为不寻常结构单元的形成和结合提供了一个新的范例,从而进一步加深了对组装线化学的认识。