Novartis Institutes for BioMedical Research, Emeryville, CA, United States of America.
PLoS One. 2018 Mar 5;13(3):e0193851. doi: 10.1371/journal.pone.0193851. eCollection 2018.
Acinetobacter baumannii ATCC 19606 can grow without lipooligosaccharide (LOS). Lack of LOS can result from disruption of the early lipid A biosynthetic pathway genes lpxA, lpxC or lpxD. Although LOS itself is not essential for growth of A. baumannii ATCC 19606, it was previously shown that depletion of the lipid A biosynthetic enzyme LpxK in cells inhibited growth due to the toxic accumulation of lipid A pathway intermediates. Growth of LpxK-depleted cells was restored by chemical inhibition of LOS biosynthesis using CHIR-090 (LpxC) and fatty acid biosynthesis using cerulenin (FabB/F) and pyridopyrimidine (acetyl-CoA-carboxylase). Here, we expand on this by showing that inhibition of enoyl-acyl carrier protein reductase (FabI), responsible for converting trans-2-enoyl-ACP into acyl-ACP during the fatty acid elongation cycle also restored growth during LpxK depletion. Inhibition of fatty acid biosynthesis during LpxK depletion rescued growth at 37°C, but not at 30°C, whereas rescue by LpxC inhibition was temperature independent. We exploited these observations to demonstrate proof of concept for a targeted medium-throughput growth restoration screening assay to identify small molecule inhibitors of LOS and fatty acid biosynthesis. The differential temperature dependence of fatty acid and LpxC inhibition provides a simple means by which to separate growth stimulating compounds by pathway. Targeted cell-based screening platforms such as this are important for faster identification of compounds inhibiting pathways of interest in antibacterial discovery for clinically relevant Gram-negative pathogens.
鲍曼不动杆菌 ATCC 19606 可以在没有脂寡糖 (LOS) 的情况下生长。LOS 的缺乏可能是由于早期脂质 A 生物合成途径基因 lpxA、lpxC 或 lpxD 的破坏。尽管 LOS 本身对于鲍曼不动杆菌 ATCC 19606 的生长不是必需的,但先前的研究表明,细胞中脂质 A 生物合成酶 LpxK 的耗尽会由于脂质 A 途径中间产物的毒性积累而抑制生长。LpxK 耗尽细胞的生长可以通过使用 CHIR-090(LpxC)抑制 LOS 生物合成和使用 cerulenin(FabB/F)和吡啶嘧啶(乙酰辅酶 A 羧化酶)抑制脂肪酸生物合成来恢复。在这里,我们通过表明负责在脂肪酸延长循环中将反式 2-烯酰-ACP 转化为酰基-ACP 的烯酰-ACP 还原酶 (FabI) 的抑制也可以在 LpxK 耗尽时恢复生长来扩展这一点。在 LpxK 耗尽期间,脂肪酸生物合成的抑制挽救了 37°C 下的生长,但不能挽救 30°C 下的生长,而 LpxC 抑制的挽救与温度无关。我们利用这些观察结果证明了针对 LOS 和脂肪酸生物合成的靶向高通量生长恢复筛选测定的概念验证,以鉴定 LOS 和脂肪酸生物合成的小分子抑制剂。脂肪酸和 LpxC 抑制的差异温度依赖性为通过途径分离生长刺激化合物提供了一种简单的方法。这种靶向基于细胞的筛选平台对于更快地鉴定在针对临床相关革兰氏阴性病原体的抗菌发现中抑制感兴趣途径的化合物非常重要。