Santini Joanne M, vanden Hoven Rachel N
Department of Microbiology, La Trobe University, 3086 Victoria, Australia.
J Bacteriol. 2004 Mar;186(6):1614-9. doi: 10.1128/JB.186.6.1614-1619.2004.
The chemolithoautotroph NT-26 oxidizes arsenite to arsenate by using a periplasmic arsenite oxidase. Purification and preliminary characterization of the enzyme revealed that it (i) contains two heterologous subunits, AroA (98 kDa) and AroB (14 kDa); (ii) has a native molecular mass of 219 kDa, suggesting an alpha2beta2 configuration; and (iii) contains two molybdenum and 9 or 10 iron atoms per alpha2beta2 unit. The genes that encode the enzyme have been cloned and sequenced. Sequence analyses revealed similarities to the arsenite oxidase of Alcaligenes faecalis, the putative arsenite oxidase of the beta-proteobacterium ULPAs1, and putative proteins of Aeropyrum pernix, Sulfolobus tokodaii, and Chloroflexus aurantiacus. Interestingly, the AroA subunit was found to be similar to the molybdenum-containing subunits of enzymes in the dimethyl sulfoxide reductase family, whereas the AroB subunit was found to be similar to the Rieske iron-sulfur proteins of cytochrome bc1 and b6f complexes. The NT-26 arsenite oxidase is probably exported to the periplasm via the Tat secretory pathway, with the AroB leader sequence used for export. Confirmation that NT-26 obtains energy from the oxidation of arsenite was obtained, as an aroA mutant was unable to grow chemolithoautotrophically with arsenite. This mutant could grow heterotrophically in the presence of arsenite; however, the arsenite was not oxidized to arsenate.
化能无机自养菌NT - 26通过周质亚砷酸盐氧化酶将亚砷酸盐氧化为砷酸盐。该酶的纯化及初步特性分析表明：（i）它包含两个异源亚基，AroA（98 kDa）和AroB（14 kDa）；（ii）天然分子量为219 kDa，表明为α2β2结构；（iii）每个α2β2单元含有两个钼原子和9个或10个铁原子。编码该酶的基因已被克隆和测序。序列分析显示，其与粪产碱杆菌的亚砷酸盐氧化酶、β - 变形菌ULPAs1的假定亚砷酸盐氧化酶以及嗜火栖热菌、嗜热栖热硫化叶菌和橙黄嗜热栖热放线菌的假定蛋白具有相似性。有趣的是，发现AroA亚基与二甲基亚砜还原酶家族中酶的含钼亚基相似，而AroB亚基与细胞色素bc1和b6f复合物的 Rieske 铁硫蛋白相似。NT - 26亚砷酸盐氧化酶可能通过Tat分泌途径输出到周质，其中AroB前导序列用于输出。由于aroA突变体不能利用亚砷酸盐进行化能无机自养生长，从而证实了NT - 26从亚砷酸盐氧化中获取能量。该突变体在有亚砷酸盐存在的情况下能够进行异养生长；然而，亚砷酸盐未被氧化为砷酸盐。
