ABSTRACT
The tripeptide backbone of phosphinothricin (PT) tripeptide (PTT), a compound with herbicidal activity from
Streptomyces viridochromogenes
, is assembled by three stand-alone peptide synthetase modules. The enzyme PhsA (66 kDa) recruits the PT-precursor
N
-acetyl-demethylphosphinothricin (
N
-Ac-DMPT), whereas the two alanine residues of PTT are assembled by the enzymes PhsB and PhsC (129 and 119 kDa, respectively). During or after assembly, the N-Ac-DMPT residue in the peptide is converted to PT by methylation and deacetylation. Both
phsB
and
phsC
appear to be cotranscribed together with two other genes from a single promoter and they are located at a distance of 20 kb from the gene
phsA
, encoding PhsA, in the PTT biosynthesis gene cluster of
S. viridochromogenes
. PhsB and PhsC represent single nonribosomal peptide synthetase elongation modules lacking a thioesterase domain. Gene inactivations, genetic complementations, determinations of substrate specificity of the heterologously produced proteins, and comparison of PhsC sequence with the amino terminus of the alanine-activating nonribosomal peptide synthetase PTTSII from
S. viridochromogenes
confirmed the role of the two genes in the bialanylation of Ac-DMPT. The lack of an integral thioesterase domain in the PTT assembly system points to product release possibly involving two type II thioesterase genes (
the1
and
the2
) located in the PTT gene cluster alone or in conjunction with an as yet unknown mechanism of product release.
摘要
一种具有除草活性的化合物--phosphinothricin(PT)三肽(PTT)的三肽骨架来自于
链霉菌(Streptomyces viridochromogenes
由三个独立的肽合成酶模块组装而成。酶 PhsA(66 kDa)招募 PT 前体
N
-乙酰基-去甲基磷霉素(N
N
-Ac-DMPT),而 PTT 的两个丙氨酸残基则由 PhsB 和 PhsC 酶(分别为 129 和 119 kDa)组装。在组装过程中或组装后,肽中的 N-Ac-DMPT 残基会通过甲基化和去乙酰化转化为 PT。两个
phsB
和
phsC
似乎与另外两个基因共同转录自一个启动子,它们与基因
phsA
的距离为 20 kb。
病毒色素
.PhsB 和 PhsC 代表缺乏硫酯酶结构域的单一非核糖体肽合成酶延伸模块。基因失活、基因互补、确定异源生产的蛋白质的底物特异性,以及将 PhsC 序列与来自 S. viridochromogenes 的丙氨酸活化非核糖体肽合成酶 PTTSII 的氨基末端进行比较。
的丙氨酸活化非核糖体肽合成酶 PTTSII
证实了这两个基因在 Ac-DMPT 的双乙酰化过程中的作用。PTT 组装系统中缺乏一个完整的硫酯酶结构域,这表明产物的释放可能涉及两个 II 型硫酯酶基因(the1和the2)。
和
和
2
)单独或与一种尚不清楚的产物释放机制共同作用。