Genome-Based Discovery of a Novel Membrane-Bound 1,6-Dihydroxyphenazine Prenyltransferase from a Marine Actinomycete

Recently, novel prenylated derivatives of 1,6-dihydroxyphenazine have been isolated from the marine sponge-associated Streptomyces sp. SpC080624SC-11. Genome sequencing of this strain now revealed a gene cluster containing all genes necessary for the synthesis of the phenazine and the isoprenoid moieties. Unexpectedly, however, the cluster did not contain a gene with similarity to previously investigated phenazine prenyltransferases, but instead a gene with modest similarity to the membrane-bound prenyltransferases of ubiquinone and menaquinone biosynthesis. Expression of this gene in E. coli and isolation of the membrane fraction proved that the encoded enzyme, Mpz10, catalyzes two successive prenylations of 1,6-dihydroxyphenazine. Mpz10 is the first example of a membrane-bound enzyme catalyzing the prenylation of a phenazine substrate, and one of few examples of membrane-bound enzymes involved in the prenylation of aromatic secondary metabolites in microorganisms.近期，研究人员从与海洋海绵共生的链霉菌属（Streptomyces sp.）菌株SpC080624SC-11中，分离得到了1,6-二羟基吩嗪（1,6-dihydroxyphenazine）的新型异戊烯基化衍生物。对该菌株进行基因组测序后发现，其携带的一个基因簇（gene cluster）包含合成吩嗪骨架与类异戊二烯结构单元（isoprenoid moieties）所需的全部基因。然而令人意外的是，该基因簇并未包含此前已被研究的吩嗪异戊烯基转移酶（phenazine prenyltransferases）同源基因，而是存在一个与泛醌（ubiquinone）、甲基萘醌（menaquinone）生物合成途径中的膜结合型异戊烯基转移酶（membrane-bound prenyltransferases）具有中等同源性的基因。将该基因在大肠杆菌（E. coli）中进行异源表达，并分离得到膜组分（membrane fraction）后，实验证实其编码的酶Mpz10可催化1,6-二羟基吩嗪的两次连续异戊烯基化反应。Mpz10是首个被发现可催化吩嗪类底物异戊烯基化的膜结合酶，同时也是微生物（microorganisms）中参与芳香族次级代谢产物（aromatic secondary metabolites）异戊烯基化的少数膜结合酶之一。