Harayama S, Rekik M
Department of Medical Biochemistry, University Medical Center, Geneva, Switzerland.
J Biol Chem. 1989 Sep 15;264(26):15328-33.
Dioxygenases that catalyze the cleavage of the aromatic ring are classified into two groups according to their mode of ring fission. Substrates of ring-cleavage dioxygenases usually contain hydroxyl groups on adjacent aromatic carbons, and intradiol enzymes cleave the ring between these two hydroxyl groups. Extradiol enzymes in contrast cleave the ring between one hydroxylated carbon and its adjacent nonhydroxylated carbon. In this study, we determined the complete nucleotide sequence of nahC, the structural gene for 1,2-dihydroxynaphthalene dioxygenase encoded in the NAH7 plasmid of Pseudomonas putida. This enzyme is an extradiol ring-cleavage enzyme that cleaves the first ring of 1,2-dihydroxynaphthalene. The amino acid sequence of the dioxygenase deduced from the DNA sequence demonstrated that the molecular weight of the enzyme is 33,882. This result was in agreement with those of maxicell analyses that showed that the nahC product was a 36-kDa protein. Interestingly, the amino acid sequence of 1,2-dihydroxynaphthalene dioxygenase was 50% homologous with that of 2,3-dihydroxybiphenyl dioxygenase, which catalyzes extradiol cleavage of the first ring of 2,3-dihydroxybiphenyl (Furukawa, K., Arimura, N., and Miyazaki, T. (1987) J. Bacteriol. 169, 427-429). The amino acid sequence similarity of 1,2-dihydroxynaphthalene dioxygenase with catechol 2,3-dioxygenase, which is an authentic extradiol dioxygenase, was rather low (16%). However, a statistical analysis by the method of S. B. Needleman and C. D. Wunsch [1970) J. Mol. Biol. 48, 443-453) clearly showed that these two dioxygenases are evolutionarily related. Therefore, these extradiol enzymes are considered as products of the same gene superfamily. From the significant sequence similarity between intradiol enzymes, it has been shown (Neidle, E. L., Harnett, C., Bonitz, S., and Ornston, L. N. (1988) J. Bacteriol. 170, 4874-4880) that intradiol enzymes evolved from a common ancestor. Comparison of the amino acid sequence of extradiol enzymes with those of intradiol dioxygenases did not show any significant global or localized similarity.
催化芳香环裂解的双加氧酶根据其环裂变模式可分为两类。环裂解双加氧酶的底物通常在相邻的芳香族碳原子上含有羟基，内二醇酶在这两个羟基之间裂解环。相比之下，外二醇酶在一个羟基化碳与其相邻的非羟基化碳之间裂解环。在本研究中，我们确定了恶臭假单胞菌NAH7质粒中编码的1,2-二羟基萘双加氧酶的结构基因nahC的完整核苷酸序列。这种酶是一种外二醇环裂解酶，可裂解1,2-二羟基萘的第一个环。从DNA序列推导的双加氧酶的氨基酸序列表明，该酶的分子量为33,882。这一结果与最大细胞分析结果一致，最大细胞分析表明nahC产物是一种36 kDa的蛋白质。有趣的是，1,2-二羟基萘双加氧酶的氨基酸序列与催化2,3-二羟基联苯第一个环的外二醇裂解的2,3-二羟基联苯双加氧酶的氨基酸序列同源性为50%。1,2-二羟基萘双加氧酶与真正的外二醇双加氧酶儿茶酚2,3-双加氧酶的氨基酸序列相似性相当低（16%）。然而，S. B. Needleman和C. D. Wunsch [1970年，《分子生物学杂志》48卷，443 - 453页]方法的统计分析清楚地表明这两种双加氧酶在进化上相关。因此，这些外二醇酶被认为是同一基因超家族的产物。从内二醇酶之间显著的序列相似性已表明（Neidle, E. L., Harnett, C., Bonitz, S., and Ornston, L. N. (1988) J. Bacteriol. 170, 4874 - 4880）内二醇酶起源于一个共同的祖先。外二醇酶与内二醇双加氧酶的氨基酸序列比较未显示出任何显著的全局或局部相似性。
