Werlen C, Kohler H P, van der Meer J R
Department of Microbiology, Swiss Federal Institute for Environmental Science and Technology (EAWAG), CH-8600 Duebendorf, Switzerland.
J Biol Chem. 1996 Feb 23;271(8):4009-16. doi: 10.1074/jbc.271.8.4009.
The chlorobenzene degradation pathway of Pseudomonas sp. strain P51 is an evolutionary novelty. The first enzymes of the pathway, the chlorobenzene dioxygenase and the cis-chlorobenzene dihydrodiol dehydrogenase, are encoded on a plasmid-located transposon Tn5280. Chlorobenzene dioxygenase is a four-protein complex, formed by the gene products of tcbAa for the large subunit of the terminal oxygenase, tcbAb for the small subunit, tcbAc for the ferredoxin, and tcbAd for the NADH reductase. Directly downstream of tcbAd is the gene for the cis-chlorobenzene dihydrodiol dehydrogenase, tcbB. Homology comparisons indicated that these genes and gene products are most closely related to those for toluene (todC1C2BAD) and benzene degradation (bedC1C2BA and bnzABCD) and distantly to those for biphenyl, naphthalene, and benzoate degradation. Similar to the tod-encoded enzymes, chlorobenzene dioxygenase and cis-chlorobenzene dihydrodiol dehydrogenase were capable of oxidizing 1,2-dichlorobenzene, toluene, naphthalene, and biphenyl, but not benzoate, to the corresponding dihydrodiol and dihydroxy intermediates. These data strongly suggest that the chlorobenzene dioxygenase and dehydrogenase originated from a toluene or benzene degradation pathway, probably by horizontal gene transfer. This evolutionary event left its traces as short gene fragments directly outside the tcbAB coding regions.
假单胞菌属菌株P51的氯苯降解途径是一种进化上的新现象。该途径的首批酶，即氯苯双加氧酶和顺式氯苯二氢二醇脱氢酶，由位于质粒上的转座子Tn5280编码。氯苯双加氧酶是一种四蛋白复合体，由末端加氧酶大亚基的tcbAa基因产物、小亚基的tcbAb、铁氧还蛋白的tcbAc以及NADH还原酶的tcbAd组成。tcbAd的直接下游是顺式氯苯二氢二醇脱氢酶的基因tcbB。同源性比较表明，这些基因及其产物与甲苯（todC1C2BAD）和苯降解（bedC1C2BA和bnzABCD）的基因及其产物关系最为密切，与联苯、萘和苯甲酸降解的基因及其产物关系较远。与tod编码的酶类似，氯苯双加氧酶和顺式氯苯二氢二醇脱氢酶能够将1,2 - 二氯苯、甲苯、萘和联苯氧化为相应的二氢二醇和二羟基中间体，但不能氧化苯甲酸。这些数据有力地表明，氯苯双加氧酶和脱氢酶可能通过水平基因转移起源于甲苯或苯降解途径。这一进化事件在tcbAB编码区域之外留下了短基因片段作为痕迹。
