Cloning and analysis of geldanamycin partial biosynthetic gene cluster of Streptomyces hygroscopicus 17997 / 生物工程学报

ABSTRACT

A geldanamycin (GDM) producing strain, Streptomyces hygroscopicus 17997, was isolated from Yunnan China soil by our institute researchers. GDM is an ansamycin antibiotic, which has the ability to bind with Hsp90 (Heat Shock Protein 90) and alter its function. Hsp90 is a chaperone protein involved in the regulation of the cell cycle, cell growth, cell survival, apoptosis, and oncogenesis. So it plays a key role in regulating the physiology of cells exposed to environmental stress and in maintaining the malignant phenotype of tumor cells. As an inhibitor of Hsp90, GDM possesses potent antitumor and antivirus bioactivity, but the hypato-toxicity and poor solubility in water limits its clinical use. Two GDM derivatives, 17-(Allylamino)-17-demethoxygeldanamycin (17-AAG) and 17-dimethylamino-ethylamino-17-demethoxygeldanamycin (17-DMAG), both showing lesser hepato-toxicity, are now in Phase II and Phase I clinic trials. In order to accomplish the structure modification of GDM by genetic means, an attempt to obtain the biosynthetic gene cluster of GDM from S. hygroscopicus 17997 was made. In this study, a pair of primers was designed according to a conserved sequence of one of possible post-PKS (polyketides synthase) modification genes, the carbamoyltransferase (CT) gene (gdmN) in GDM biosynthesis. The 732 bp PCR product was obtained from the S. hygroscopicus 17997 genomic DNA. Through the colony-PCR Binary Search Method, using the CT gene primers, six positive cosmid clones, CT1-6, were identified from the S. hygroscopicus 17997 cosmid genomic library. The CT gene containing fragments were verified and localized by Southern blot. The CT-4 positive cosmid was then sub-cloned and sequenced. Approximately 28.356kb of foreign gene sequence from CT-4 cosmid and by further PCR extension reaction was obtained. Based on BLAST analysis, this sequence contains 13 possible ORFs and their deduced functions are believed to be involved in GDM production. The ORF1 encoding products show homology (87%) with incomplete sixth module and complete seventh module of PKS, gdmA3, in S. hygroscopicus NRRL 3602. The ORF2-13 gene products are similar to gdmF(9 5%), gdmM(8 8%), gdmN (92%), gdmH (92%), I (93%), J (90%), K (93%), G (96%), gdmO (91%), gdmP (93%) and two transcription regulation genes gdmRI (83%) and gdmRII (90%). The obtained possible GDM biosynthetic gene cluster in S. hygroscopicus 17997 will facilitate the further functional analysis of the genes and to modify the structure of GDM through combinatorial biosynthesis.