ABSTRACT
1
H
-3-hydroxy-4-oxoquinoline 2,4-dioxygenase (Qdo) from
Pseudomonas putida
33/1 and 1
H
-3-hydroxy-4-oxoquinaldine 2,4-dioxygenase (Hod) from
Arthrobacter ilicis
Rü61a catalyze an N-heterocyclic-ring cleavage reaction, generating
N
-formylanthranilate and
N
-acetylanthranilate, respectively, and carbon monoxide. Amino acid sequence comparisons between Qdo, Hod, and a number of proteins belonging to the α/β hydrolase-fold superfamily of enzymes and analysis of the similarity between the predicted secondary structures of the 2,4-dioxygenases and the known secondary structure of haloalkane dehalogenase from
Xanthobacter autotrophicus
GJ10 strongly suggested that Qdo and Hod are structurally related to the α/β hydrolase-fold enzymes. The residues S95 and H244 of Qdo were found to be arranged like the catalytic nucleophilic residue and the catalytic histidine, respectively, of the α/β hydrolase-fold enzymes. Investigation of the potential functional significance of these and other residues of Qdo through site-directed mutagenesis supported the hypothesis that Qdo is structurally as well as functionally related to serine hydrolases, with S95 being a possible catalytic nucleophile and H244 being a possible catalytic base. A hypothetical reaction mechanism for Qdo-catalyzed 2,4-dioxygenolysis, involving formation of an ester bond between the catalytic serine residue and the carbonyl carbon of the substrate and subsequent dioxygenolysis of the covalently bound anionic intermediate, is discussed.
摘要
1
H
-3-羟基-4-氧代喹啉 2,4-二氧化酶(Qdo)
假单胞菌
33/1 和 1
H
-3-羟基-4-氧代喹啉 2,4-二加氧酶(Hod)
Arthrobacter ilicis
Rü61a 催化 N-杂环环裂解反应,生成
N
-甲酰邻氨基苯甲酸酯和
N
-和一氧化碳。对 Qdo、Hod 和一些属于α/β水解酶-折叠超家族酶的蛋白质进行了氨基酸序列比较,并分析了预测的 2,4-二氧合酶二级结构与已知的卤代烃脱卤酶二级结构之间的相似性。
自养黄杆菌
GJ10 强烈表明,Qdo 和 Hod 在结构上与 α/β 水解酶-折叠酶有关。研究发现,Qdo 的残基 S95 和 H244 的排列方式分别类似于 α/β 水解折叠酶的催化亲核残基和催化组氨酸。通过定点突变研究 Qdo 这些残基和其他残基的潜在功能意义,支持了 Qdo 在结构上和功能上与丝氨酸水解酶相关的假设,其中 S95 可能是催化亲核残基,H244 可能是催化碱基。本文讨论了 Qdo 催化 2,4-二氧分解的假定反应机制,包括催化丝氨酸残基与底物的羰基碳之间形成酯键,以及随后共价结合的阴离子中间体的二氧分解。