Palmer C N, Axen E, Hughes V, Wolf C R
Biomedical Research Centre and ICRF Molecular Pharmacology Unit, Ninewells Hospital and Medical School, Dundee DD1 9SY, United Kingdom.
J Biol Chem. 1998 Jul 17;273(29):18109-16. doi: 10.1074/jbc.273.29.18109.
Bm3R1 is a helix-turn-helix transcriptional repressor from Bacillus megaterium whose binding to DNA is inhibited by fatty acids and a wide range of compounds that modulate lipid metabolism. The inactivation of Bm3R1/DNA binding activity results in the activation of transcription of the operon encoding a fatty acid hydroxylase, cytochrome P450 102. The metabolic role of this operon is unknown. It is possible that it is involved in the synthesis of modified fatty acids as part of normal cellular metabolism or may represent a protective mechanism by which B. megaterium detoxifies harmful foreign lipids. In this report we demonstrate that polyunsaturated fatty acids (PUFA) activate the transcription of the CYP102 operon. These PUFA are the most potent activators of the CYP102 operon observed to date, and we show that their effects are due to binding directly to Bm3R1. In addition, cultures that have been treated with the CYP102 inducer, nafenopin, are protected against PUFA toxicity. Resistance to PUFA toxicity is also seen in a Bm3R1-deficient strain that constitutively expresses CYP102. The resistant phenotype of this Bm3R1 mutant strain is reversed by specific chemical inactivation of CYP102. These data demonstrate that Bm3R1 can act as a direct sensor of toxic fatty acids and, in addition, provide the first direct evidence of fatty acids binding to a prokaryotic transcription factor.
Bm3R1是一种来自巨大芽孢杆菌的螺旋-转角-螺旋转录抑制因子，其与DNA的结合受到脂肪酸以及多种调节脂质代谢的化合物的抑制。Bm3R1/DNA结合活性的失活会导致编码脂肪酸羟化酶细胞色素P450 102的操纵子转录激活。该操纵子的代谢作用尚不清楚。有可能它参与了作为正常细胞代谢一部分的修饰脂肪酸的合成，或者可能代表了巨大芽孢杆菌对有害外来脂质进行解毒的一种保护机制。在本报告中，我们证明多不饱和脂肪酸（PUFA）可激活CYP102操纵子的转录。这些PUFA是迄今为止观察到的CYP102操纵子最有效的激活剂，并且我们表明它们的作用是由于直接与Bm3R1结合。此外，用CYP102诱导剂萘酚平处理过的培养物对PUFA毒性具有抗性。在组成型表达CYP102的Bm3R1缺陷型菌株中也观察到对PUFA毒性的抗性。通过CYP102的特异性化学失活，该Bm3R1突变菌株的抗性表型得以逆转。这些数据表明Bm3R1可以作为有毒脂肪酸的直接传感器，此外，还提供了脂肪酸与原核转录因子结合的首个直接证据。
