ABSTRACT
Four
Rhodococcus
spp. exhibited the ability to use 4,4′-dithiodibutyric acid (DTDB) as a sole carbon source for growth. The most important step for the production of a novel polythioester (PTE) using DTDB as a precursor substrate is the initial cleavage of DTDB. Thus, identification of the enzyme responsible for this step was mandatory. Because
Rhodococcus erythropolis
strain MI2 serves as a model organism for elucidation of the biodegradation of DTDB, it was used to identify the genes encoding the enzymes involved in DTDB utilization. To identify these genes, transposon mutagenesis of
R. erythropolis
MI2 was carried out using transposon pTNR-TA. Among 3,261 mutants screened, 8 showed no growth with DTDB as the sole carbon source. In five mutants, the insertion locus was mapped either within a gene coding for a polysaccharide deacetyltransferase, a putative ATPase, or an acetyl coenzyme A transferase, 1 bp upstream of a gene coding for a putative methylase, or 176 bp downstream of a gene coding for a putative kinase. In another mutant, the insertion was localized between genes encoding a putative transcriptional regulator of the TetR family (
noxR
) and an NADH:flavin oxidoreductase (
nox
). Moreover, in two other mutants, the insertion loci were mapped within a gene encoding a hypothetical protein in the vicinity of
noxR
and
nox
. The interruption mutant generated,
R. erythropolis
MI2
nox
Ω
tsr
, was unable to grow with DTDB as the sole carbon source. Subsequently,
nox
was overexpressed and purified, and its activity with DTDB was measured. The specific enzyme activity of Nox amounted to 1.2 ± 0.15 U/mg. Therefore, we propose that Nox is responsible for the initial cleavage of DTDB into 2 molecules of 4-mercaptobutyric acid (4MB).
摘要
四种
Rhodococcus
表现出利用 4,4′-二硫代二丁酸(DTDB)作为唯一碳源进行生长的能力。使用 DTDB 作为前体底物生产新型聚硫醚(PTE)的最重要步骤是 DTDB 的初始裂解。因此,必须确定负责这一步骤的酶。因为
红球菌
菌株 MI2 作为阐明 DTDB 生物降解的模式生物,被用来鉴定编码参与 DTDB 利用的酶的基因。为了确定这些基因,对红腹灰质酵母进行了转座子诱变。
R. erythropolis
MI2 的转座子诱变。在筛选出的 3261 个突变体中,有 8 个突变体在以 DTDB 为唯一碳源时不生长。在 5 个突变体中,插入基因座位于多糖脱乙酰转移酶、假定 ATP 酶或乙酰辅酶 A 转移酶的编码基因内,假定甲基酶的编码基因上游 1 bp 处,或假定激酶的编码基因下游 176 bp 处。在另一个突变体中,插入定位在编码 TetR 家族推定转录调节因子(noxR)的基因之间。
noxR
)和 NADH:黄素氧化还原酶(noxR
nox
).此外,在另外两个突变体中,插入位点被定位在一个编码假定蛋白的基因内,该基因与
noxR
和
nox
.产生的中断突变体、
R. erythropolis
MI2
nox
Ω
tsr
在以 DTDB 为唯一碳源的情况下无法生长。随后
nox
的活性进行了测定。Nox 的比酶活性为 1.2 ± 0.15 U/mg 。因此,我们认为 Nox 负责将 DTDB 初步裂解为 2 个分子的 4-巯基丁酸(4MB)。