Asm8, a specific LAL-type activator of 3-amino-5-hydroxy-benzoate biosynthesis in ansamitocin production

• Published in: 中国科学：生命科学英文版 2013 (7), p.601-608
• Main Author: PAN WenQin KANG QianJin WANG Lei BAI LinQuan DENG ZiXin
• Format: Article
• Language: English
• Subjects: AL型; 氨基酸; 活化剂; 生产商; 生物合成基因簇; 短管赤眼蜂; 羟基苯甲酸; 苯甲酸酯
• ISSN: 1674-7305; 1869-1889

The highly potent antitumor agent ansamitocin P3 is a macrolactam isolated from Actinosynnema pretiosum ATCC 31565. A 120-kb DNA fragment was previously identified as the ansamitocin biosynthetic gene cluster, and contains genes for polyketide assembly, precursor synthesis, post-polyketide synthesis modification, and regulation. Within the biosynthetic gene cluster, asm8 encodes an 1117-amino-acid protein with a high degree of similarity to the large ATP-binding LuxR family-type regulators. In the current study, we determined that inactivation of asm8 by gene replacement in ATCC 31565 resulted in the complete loss of ansamitocin production, and that complementation with a cloned asm8 gene restored ansamitocin biosynthesis. Interestingly, the disruption of asm8 decreased the transcription of genes responsible for 3-amino-5-hydroxybenzoate （AHBA） formation, the starter unit required for ansamitocin biosynthesis. Subsequently, feeding of exogenous AHBA to the asm8 mutant restored ansamitocin biosynthesis, which showed that Asm8 is a specific positive regulator in AHBA biosynthesis. In addition, investigation of asm8 homologs identified two new ansamitocin producers, and inactivation of the asm8 homolog in A. pretiosum ATCC 31280 abolished ansamitocin production in this strain. Characterization of the positive regulator Asm8 and discovery of the two new ansamitocin producers paves the way for further improving production of this important antitumor agent.