Arginine racemization by coupled catabolic and anabolic dehydrogenases
Arginine racemization by coupled catabolic and anabolic dehydrogenases
复制标题
DOI：
10.1073/pnas.0808269106
复制
发表时间：
2009-01-20
影响因子：
11.1
通讯作者：
Lu, Chung-Dar
中科院分区：
文献类型：
--
作者：
Li, Congran;Lu, Chung-Dar
D-氨基酸存在于生物体中，作为许多不同机器的专门成分。由主要L-对映体的外消旋化生物合成D-氨基酸由单一酶催化。本文报道了铜绿假单胞菌D-精氨酸代谢中一种新的双组分氨基酸消旋酶的发现。从DNA微阵列分析，推定的dauBAR操纵子（D-精氨酸利用）的未知功能被发现是高度诱导的D-精氨酸。dau操纵子在D-精氨酸代谢中的重要性通过dauA或dauB损伤的菌株不能使用D-精氨酸作为唯一碳源的发现来证明。两条证据表明DauA和DauB是精氨酸D-至-L外消旋化所必需的。首先，D-精氨酸对L-精氨酸营养缺陷型的生长互补作用被dauA或dauB的病变所消除。第二，D-精氨酸诱导L-精氨酸特异性基因的亲本菌株PAO 1，但不是在其dauA或dauB突变体。纯化酶的活性测量进一步支持了这一假设：DauA催化D-精氨酸氧化脱氨为2-酮精氨酸和氨，DauB能够使用2-酮精氨酸和氨作为底物，并在NADPH或NADH存在下将其转化为L-精氨酸。因此，我们认为DauA和DauB是偶联的分解代谢和合成代谢酶，以进行精氨酸的D-到-L外消旋化，这是通过L-精氨酸分解代谢途径利用D-精氨酸的先决条件。
D-Amino acids exist in living organisms as specialized components of many different machineries. Biosynthesis of D-amino acids from racemization of predominant L-enantiomers is catalyzed by a single enzyme. Here, we report the finding of a novel 2-component amino acid racemase for D-to-L inversion in D-arginine metabolism of Pseudomonas aeruginosa. From DNA microarray analysis, the putative dauBAR operon (for D-arginine utilization) of unknown functions was found to be highly induced by D-arginine. The importance of the dau operon in D-arginine metabolism was demonstrated by the findings that strains with a lesion at dauA or dauB failed to use D-arginine as sole carbon source. Two lines of evidence suggest that DauA and DauB are required for D-to-L racemization of arginine. First, growth complementation of an L-arginine auxotroph by D-arginine was abolished by a lesion at dauA or dauB. Second, D-arginine induced L-arginine-specific genes in the parental strain PAO1 but not in its dauA or dauB mutants. This hypothesis was further supported by activity measurements of the purified enzymes: DauA catalyzes oxidative deamination of D-arginine into 2-ketoarginine and ammonia, and DauB is able to use 2-ketoarginine and ammonia as substrates and convert them into L-arginine in the presence of NADPH or NADH. Thus, we propose that DauA and DauB are coupled catabolic and anabolic dehydrogenases to perform D-to-L racemization of arginine, which serves as prerequisite of D-arginine utilization through L-arginine catabolic pathways.