Nishizawa Tomoyasu, Asayama Munehiko, Shirai Makoto
The United Graduate School, Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183-8509, Japan3.
Laboratory of Molecular Genetics, School of Agriculture1, and Gene Research Center2, Ibaraki University, Ami, Ibaraki 300-0393, Japan.
Microbiology (Reading). 2001 May;147(Pt 5):1235-1241. doi: 10.1099/00221287-147-5-1235.
It was demonstrated previously that the operon consisting of the non-ribosomal peptide synthetase (NRPS) gene coupled with the polyketide synthase (PKS) gene involved in cyclic heptapeptide microcystin synthesis includes two different D-amino acid synthetase genes, an epimerization domain at the 3' end of module 2, and the racemase gene mcyF. To determine the role of mcyF in microcystin synthesis, gene-disruption and complementation analyses were carried out. Insertional mutagenesis in the mcyF gene, generated by homologous recombination, abolished only microcystin synthesis, but did not influence cell growth. Furthermore, McyF supported D-Glu-independent growth of a strain of Escherichia coli defective in D-Glu synthesis. It is concluded that mcyF is the glutamic acid racemase gene involved in the synthesis of D-Glu residues in the microcystin molecule. This is the first report of the racemase in prokaryotic NRPS.
先前已证明，参与环状七肽微囊藻毒素合成的由非核糖体肽合成酶（NRPS）基因与聚酮合酶（PKS）基因组成的操纵子包含两个不同的D-氨基酸合成酶基因、模块2 3'端的差向异构化结构域以及消旋酶基因mcyF。为了确定mcyF在微囊藻毒素合成中的作用，进行了基因破坏和互补分析。通过同源重组在mcyF基因中产生的插入诱变仅消除了微囊藻毒素的合成，但不影响细胞生长。此外，McyF支持一株D-谷氨酸合成缺陷的大肠杆菌菌株在不依赖D-谷氨酸的情况下生长。得出的结论是，mcyF是参与微囊藻毒素分子中D-谷氨酸残基合成的谷氨酸消旋酶基因。这是原核NRPS中消旋酶的首次报道。
