Ajinomoto-Genetika Research Institute, 1st Dorozhny pr. 1, Moscow, 113545, Russia.
Microbiologyopen. 2013 Jun;2(3):471-81. doi: 10.1002/mbo3.87. Epub 2013 Apr 2.
A unique operon structure has been identified in the genomes of several plant- and insect-associated bacteria. The distinguishing feature of this operon is the presence of tandem hilA and hilB genes encoding dioxygenases belonging to the PF13640 and PF10014 (BsmA) Pfam families, respectively. The genes encoding HilA and HilB from Pantoea ananatis AJ13355 were cloned and expressed in Escherichia coli. The culturing of E. coli cells expressing hilA (E. coli-HilA) or both hilA and hilB (E. coli-HilAB) in the presence of l-isoleucine resulted in the conversion of l-isoleucine into two novel biogenic compounds: l-4'-isoleucine and l-4,4'-dihydroxyisoleucine, respectively. In parallel, two novel enzymatic activities were detected in the crude cell lysates of the E. coli-HilA and E. coli-HilAB strains: l-isoleucine, 2-oxoglutarate: oxygen oxidoreductase (4'-hydroxylating) (HilA) and l-4'-hydroxyisoleucine, 2-oxoglutarate: oxygen oxidoreductase (4-hydroxylating) (HilB), respectively. Two hypotheses regarding the physiological significance of C-4(4')-hydroxylation of l-isoleucine in bacteria are also discussed. According to first hypothesis, the l-isoleucine dihydroxylation cascade is involved in synthesis of dipeptide antibiotic in P. ananatis. Another unifying hypothesis is that the C-4(4')-hydroxylation of l-isoleucine in bacteria could result in the synthesis of signal molecules belonging to two classes: 2(5H)-furanones and analogs of N-acyl homoserine lactone.
在几种与植物和昆虫相关的细菌的基因组中，已经确定了一种独特的操纵子结构。该操纵子的特征在于存在串联的 hilA 和 hilB 基因，分别编码属于 PF13640 和 PF10014（BsmA）Pfam 家族的双加氧酶。从 Pantoea ananatis AJ13355 中克隆并在大肠杆菌中表达了 HilA 和 HilB 基因。在存在 l-异亮氨酸的情况下培养表达 hilA 的大肠杆菌细胞（E. coli-HilA）或同时表达 hilA 和 hilB 的大肠杆菌细胞（E. coli-HilAB），分别将 l-异亮氨酸转化为两种新型生物合成化合物：l-4'-异亮氨酸和 l-4,4'-二羟基异亮氨酸。同时，在 E. coli-HilA 和 E. coli-HilAB 菌株的粗细胞裂解物中检测到两种新的酶活性：l-异亮氨酸、2-氧代戊二酸：氧氧化还原酶（4'-羟化）（HilA）和 l-4'-羟基异亮氨酸、2-氧代戊二酸：氧氧化还原酶（4-羟化）（HilB）。还讨论了细菌中 C-4（4'）-羟化 l-异亮氨酸的生理意义的两个假设。根据第一个假设，l-异亮氨酸二羟化级联反应参与了 P. ananatis 中二肽抗生素的合成。另一个统一的假设是，细菌中 l-异亮氨酸的 C-4（4'）-羟化可能导致属于两类信号分子的合成：2（5H）-呋喃酮和 N-酰基高丝氨酸内酯类似物。
