ABSTRACT
We have identified, cloned, and sequenced the
hca
cluster encoding the dioxygenolytic pathway for initial catabolism of 3-phenylpropionic acid (PP) in
Escherichia coli
K-12. This cluster maps at min 57.5 of the chromosome and is composed of five catabolic genes arranged as a putative operon (
hcaA1A2CBD
) and two additional genes transcribed in the opposite direction that encode a potential permease (
hcaT
) and a regulator (
hcaR
). Sequence comparisons revealed that while
hcaA1A2CD
genes encode the four subunits of the 3-phenylpropionate dioxygenase, the
hcaB
gene codes for the corresponding
cis
-dihydrodiol dehydrogenase. This type of catabolic module is homologous to those encoding class IIB dioxygenases and becomes the first example of such a catabolic cluster in
E. coli
. The inducible expression of the
hca
genes requires the presence of the
hcaR
gene product, which acts as a transcriptional activator and shows significant sequence similarity to members of the LysR family of regulators. Interestingly, the HcaA1A2CD and HcaB enzymes are able to oxidize not only PP to 3-(2,3-dihydroxyphenyl)propionate (DHPP) but also cinnamic acid (CI) to its corresponding 2,3-dihydroxy derivative. Further catabolism of DHPP requires the
mhp
-encoded
meta
fission pathway for the mineralization of 3-hydroxyphenylpropionate (3HPP) (A. Ferrández, J. L. Garcı́a, and E. Dı́az, J. Bacteriol. 179:2573–2581, 1997). Expression in
Salmonella typhimurium
of the
mhp
genes alone or in combination with the
hca
cluster allowed the growth of the recombinant bacteria in 3-hydroxycinnamic acid (3HCI) and CI, respectively. Thus, the convergent
mhp
- and
hca
-encoded pathways are also functional in
S. typhimurium
, and they are responsible for the catabolism of different phenylpropanoid compounds (3HPP, 3HCI, PP, and CI) widely available in nature.
摘要
我们鉴定、克隆并测序了
hca
簇,该簇编码大肠杆菌中 3-苯基丙酸(PP)初始分解的二氧分解途径。
大肠杆菌
K-12.该基因簇位于染色体的第 57.5 小节,由五个分解基因组成,这些基因组成了一个假定操作子(hcaA1A2CBD)。
hcaA1A2CBD
) 和另外两个反向转录的基因,这两个基因编码一种潜在的渗透酶 (
hcaT
)和一个调节器(
hcaR
).序列比较显示
hcaA1A2CD
基因编码 3-苯基丙酸二氧合酶的四个亚基,而
hcaB
基因编码相应的
顺式
-二氢二醇脱氢酶。这种分解模块与编码 IIB 类二加氧酶的模块同源,是大肠杆菌中第一个此类分解簇的实例。
大肠杆菌
.诱导表达
hca
基因的诱导表达需要
hcaR
基因产物,它是一种转录激活因子,与 LysR 家族的调节因子序列非常相似。有趣的是,HcaA1A2CD 和 HcaB 酶不仅能将 PP 氧化成 3-(2,3-二羟基苯基)丙酸(DHPP),还能将肉桂酸(CI)氧化成其相应的 2,3- 二羟基衍生物。DHPP 的进一步分解需要
mhp
-编码的
元
Ferrández, J. L. Garcı́a, and E. Dı́az, J. Bacteriol.179:2573-2581, 1997).在
鼠伤寒沙门氏菌
的
mhp
基因单独或与
hca
簇的重组细菌可分别在 3-羟基肉桂酸(3HCI)和 CI 中生长。因此,趋同的
mhp
- 和
hca
-编码的途径在
鼠伤寒杆菌
它们负责分解自然界中广泛存在的不同苯丙类化合物(3HPP、3HCI、PP 和 CI)。