ABSTRACT
In the present study, we successfully cloned a 21-kb DNA fragment containing a
d
-cycloserine (DCS) biosynthetic gene cluster from a DCS-producing
Streptomyces
lavendulae
strain, ATCC 11924. The putative gene cluster consists of 10 open reading frames (ORFs), designated
dcsA
to
dcsJ
. This cluster includes two ORFs encoding
d
-alanyl-
d
-alanine ligase (
dcsI
) and a putative membrane protein (
dcsJ
) as the self-resistance determinants of the producer organism, indicated by our previous work. When the 10 ORFs were introduced into DCS-nonproducing
Streptomyces lividans
66 as a heterologous host cell, the transformant acquired DCS productivity. This reveals that the introduced genes are responsible for the biosynthesis of DCS. As anticipated, the disruption of
dcsG
, seen in the DCS biosynthetic gene cluster, made it possible for the strain ATCC 11924 to lose its DCS production. We here propose the DCS biosynthetic pathway. First,
l
-serine is O acetylated by a
dcsE-
encoded enzyme homologous to homoserine
O
-acetyltransferase. Second,
O
-acetyl-
l
-serine accepts hydroxyurea
via
an
O
-acetylserine sulfhydrylase homolog (
dcsD
product) and forms
O
-ureido-
l
-serine. The hydroxyurea must be supplied by the catalysis of a
dcsB
-encoded arginase homolog using the
l
-arginine derivative,
N
G
-hydroxy-
l
-arginine. The resulting
O
-ureido-
l
-serine is then racemized to
O
-ureido-
d
-serine by a homolog of diaminopimelate epimerase. Finally,
O
-ureido-
d
-serine is cyclized to form DCS with the release of ammonia and carbon dioxide. The cyclization must be done by the
dcsG
or
dcsH
product, which belongs to the ATP-grasp fold family of protein.
摘要
在本研究中,我们成功克隆了一个含有
d
-环丝氨酸(DCS)生物合成基因簇的 21 kb DNA 片段。
链霉菌
菌株
菌株,即 ATCC 11924。推测基因簇由 10 个开放阅读框(ORF)组成,分别为
dcsA
到
dcsJ
.该基因簇包括两个 ORF,分别编码
d
-丙氨酰-
d
-丙氨酸连接酶 (
dcsI
)和一种假定的膜蛋白(
dcsJ
)是生产者生物的自抗性决定因子。将这 10 个 ORFs 导入不产生 DCS 的
链霉菌
66 作为异源宿主细胞时,转化体获得了 DCS 生产力。这表明引入的基因负责 DCS 的生物合成。正如预期的那样,破坏
dcsG
的破坏使 ATCC 11924 菌株失去了生产 DCS 的能力。我们在此提出 DCS 的生物合成途径。首先是
l
-丝氨酸被一个
dcsE-
编码的与高丝氨酸同源的酶进行乙酰化。
O
-乙酰转移酶。第二种、
O
-乙酰-
l
-丝氨酸通过羟基脲
通过
通过
O
-乙酰丝氨酸巯基酶同源物 (
dcsD
产物),并形成
O
-脲
l
-丝氨酸。羟基脲必须由一个
dcsB
-编码的精氨酸酶同源物利用
l
-精氨酸衍生物的催化作用来提供羟基脲、
N
G
-羟基-
l
-精氨酸。由此产生的
O
-尿苷
l
-丝氨酸消旋化为
O
-脲
d
-丝氨酸的外消旋化过程。最后
O
-尿苷
d
-丝氨酸环化形成 DCS,并释放出氨和二氧化碳。环化必须由
dcsG
或
dcsH
产物完成,它们属于 ATP-抓取折叠蛋白家族。