Funa Nobutaka, Funabashi Masanori, Yoshimura Etsuro, Horinouchi Sueharu
Department of Biotechnology, Graduate School of Agriculture and Life Sciences, the University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan.
J Biol Chem. 2005 Apr 15;280(15):14514-23. doi: 10.1074/jbc.M500190200. Epub 2005 Feb 8.
RppA is a type III polyketide synthase (PKS) that catalyzes condensation of five molecules of malonyl-CoA to form 1,3,6,8-tetrahydroxynaphthalene (THN). In Streptomyces antibioticus IFO13271 and several other Streptomyces species, an open reading frame, named momA, is present as a neighbor of rppA. MomA belonged to the "cupin" superfamily because it contained a set of two motifs that is responsible for binding one equivalent of metal ions. MomA catalyzed monooxygenation of the THN produced from malonyl-CoA by the action of RppA to form flaviolin. In addition, it used several polyketides as substrates and formed the corresponding quinones. MomA required redox-active transition metal ions (Ni(2+), Cu(2+), Fe(3+), Fe(2+), Mn(2+), and Co(2+)) for its activity, whereas it was inhibited by a redox-inert transition metal ion (Zn(2+)). MomA neither possessed any flavin prosthetic group nor required nicotinamide cofactors for monooxygenation, which shows that MomA as a member of the cupin superfamily is a novel monooxygenase. Consistent with the catalytic property of MomA, WhiE-ORFII showing similarity in amino acid sequence to MomA and containing a cupin domain also catalyzed monooxygenation of THN. whiE-ORFII is located immediately upstream of the "minimal PKS" gene within the whiE type II PKS gene cluster for biosynthesis of a gray spore pigment in Streptomyces coelicolor A3(2), and a number of whiE-ORFII homologues are present in the biosynthetic gene cluster for polyketides of type II in various Streptomyces species. These findings show that a novel class of quinone-forming monooxygenases is involved in modification of aromatic polyketides synthesized by PKSs of types II and III.
RppA是一种III型聚酮合酶（PKS），它催化五分子丙二酰辅酶A缩合形成1,3,6,8 - 四羟基萘（THN）。在抗生链霉菌IFO13271和其他几种链霉菌属物种中，一个名为momA的开放阅读框作为rppA的邻接基因存在。MomA属于“cupin”超家族，因为它包含一组负责结合一当量金属离子的两个基序。MomA催化由RppA作用于丙二酰辅酶A产生的THN的单加氧反应，形成黄素。此外，它还使用几种聚酮化合物作为底物并形成相应的醌。MomA的活性需要具有氧化还原活性的过渡金属离子（Ni(2+)、Cu(2+)、Fe(3+)、Fe(2+)、Mn(2+)和Co(2+)），而它会被氧化还原惰性的过渡金属离子（Zn(2+)）抑制。MomA既不具有任何黄素辅基，单加氧反应也不需要烟酰胺辅因子，这表明作为cupin超家族成员的MomA是一种新型单加氧酶。与MomA的催化特性一致，WhiE - ORFII在氨基酸序列上与MomA相似且包含一个cupin结构域，它也催化THN的单加氧反应。WhiE - ORFII位于天蓝色链霉菌A3(2)中用于灰色孢子色素生物合成的whiE II型PKS基因簇内“最小PKS”基因的紧邻上游，并且在各种链霉菌属物种中II型聚酮化合物的生物合成基因簇中存在许多WhiE - ORFII同源物。这些发现表明，一类新型的醌形成单加氧酶参与了由II型和III型PKS合成的芳香族聚酮化合物的修饰。
