近日，中科院南海海洋研究所鞠建华研究员团队通过基因组测序和生物信息学分析，发现灰绿霉素和绿灰霉素的生物合成基因簇结构以转运蛋白基因sgvT2为中心，上游区段负责绿灰霉素合成、下游区段负责合成绿灰霉素的域，在两个区段外则是调控基因和抗性基因区。
研究人员运用RT-PCR技术对野生型和突变株进行分析，发现它与受体的结合能够激活下游的两个SARP家族的正调控蛋白sgvT2和sgvT3，从而揭示了灰绿霉素和绿灰霉素高效协同抗菌性的生物合成机制。该成果被选为内封面文章发表在ChemBioChem上。
据介绍，灰绿霉素（Griseovridin）和绿灰霉素（Viridogrisein）是一对由多种放线菌生产的具有协同抗菌效应的链阳菌素类抗生素。灰绿霉素具有二十三元不饱和并九元含烯硫键的内酯结构，绿灰霉素具有三个天然氨基酸和五个非天然氨基酸构成的八元环脂肽结构。灰绿霉素可作用于细菌50S核糖体的A位点，阻止氨酰tRNA的结合，有利于绿灰霉素高效结合P位点，加速延生的多肽链解离，二者协同作用能显着提高抑菌效果。两种抗生素结构独特，调控机制新颖，在治疗耐药性病菌感染中具有良好的应用前景。
该研究获得了973计划项目、国家自然科学基金和中科院“百人计划”人才基金的资助。(生物谷Bioon.com)
DOI: 10.1002/cbic.201200584
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Identification of the Biosynthetic Gene Cluster and Regulatory Cascade for the Synergistic Antibacterial Antibiotics Griseoviridin and Viridogrisein in Streptomyces griseoviridis
Yunchang Xie1,2, Dr. Bo Wang1, Jing Liu1,2,Junchao Zhou1,2, Dr. Junying Ma1, Dr. Hongbo Huang1, Prof. Dr. Jianhua Ju1,*
Griseoviridin (GV) and viridogrisein (VG, also referred to as etamycin), produced by Streptomyces griseoviridis, are two chemically unrelated compounds belonging to the streptogramin family. Both of these natural products demonstrate broad-spectrum antibacterial activity and constitute excellent candidates for future drug development. To elucidate the biosynthetic machinery associated with production of these two unique antibiotics, the gene cluster responsible for both GV and VG production was identified within the Streptomyces griseoviridis genome and characterized, and its function in GV and VG biosynthesis was confirmed by inactivation of 30 genes and complementation experiments. This sgv gene cluster is localized to a 105 kb DNA region that consists of 36 open reading frames (ORFs), including four nonribosomal peptide synthetases (NRPSs) for VG biosynthesis and a set of hybrid polyketide synthases (PKS)-NRPSs with a discrete acyltransferase (AT), SgvQ, to assemble the GV backbone. The enzyme encoding genes for VG versus GV biosynthesis are separated into distinct “halves” of the cluster. A series of four genes: sgvA, sgvB, sgvC, and sgvK, were found downstream of the PKS-NRPS; these likely code for construction of a γ-butyrolactone (GBL)-like molecule. GBLs and the corresponding GBL receptor systems are the highest ranked regulators that are able to coordinate the two streptomyces antibiotic regulatory protein (SARP) family positive regulators SgvR2 and SgvR3; both are key biosynthetic activators. Models of GV, VG, and GBL biosynthesis were proposed by using functional gene assignments, determined on the basis of bioinformatics analysis and further supported by in vivo gene inactivation experiments. Overall, this work provides new insights into the biosyntheses of the GV and VG streptogramins that are potentially applicable to a host of combinatorial biosynthetic scenarios.
