Lin Yung-Feng, Yang Jianbo, Rosen Barry P
Department of Biochemistry and Molecular Biology, Wayne State University, School of Medicine, Detroit, MI 48201, USA.
J Bioenerg Biomembr. 2007 Dec;39(5-6):453-8. doi: 10.1007/s10863-007-9113-y.
The toxic metalloid arsenic is widely disseminated in the environment and causes a variety of health and environment problems. As an adaptation to arsenic-contaminated environments, organisms have developed resistance systems. Many ars operons contain only three genes, arsRBC. Five gene ars operons have two additional genes, arsD and arsA, and these two genes are usually adjacent to each other. ArsA from Escherichia coli plasmid R773 is an ATPase that is the catalytic subunit of the ArsAB As(III) extrusion pump. ArsD was recently identified as an arsenic chaperone to the ArsAB pump, transferring the trivalent metalloids As(III) and Sb(III) to the ArsA subunit of the pump. This increases the affinity of ArsA for As(III), resulting in increased rates if extrusion and resistance to environmentally relevant concentrations of arsenite. ArsD is a homodimer with three vicinal cysteine pairs, Cys12-Cys13, Cys112-Cys113 and Cys119-Cys120, in each subunit. Each vicinal pair binds one As(III) or Sb(III). ArsD mutants with alanines substituting for Cys112, Cys113, Cys119 or Cys120, individually or in pairs or truncations lacking the vicinal pairs, retained ability to interact with ArsA, to activate its ATPase activity. Cells expressing these mutants retained ArsD-enhanced As(III) efflux and resistance. In contrast, mutants with substitutions of conserved Cys12, Cys13 or Cys18, individually or in pairs, were unable to activate ArsA or to enhance the activity of the ArsAB pump. It is proposed that ArsD residues Cys12, Cys13 and Cys18, but not Cys112, Cys113, Cys119 or Cys120, are required for delivery of As(III) to and activation of the ArsAB pump.
有毒类金属砷在环境中广泛分布，会引发各种健康和环境问题。作为对砷污染环境的一种适应，生物体已形成抗性系统。许多砷抗性操纵子仅包含三个基因，即arsRBC。具有五个基因的砷抗性操纵子还有另外两个基因，arsD和arsA，且这两个基因通常彼此相邻。来自大肠杆菌质粒R773的ArsA是一种ATP酶，是ArsAB As(III)外排泵的催化亚基。ArsD最近被鉴定为ArsAB泵的砷伴侣蛋白，可将三价类金属As(III)和Sb(III)转移至泵的ArsA亚基。这增加了ArsA对As(III)的亲和力，从而提高了外排速率以及对环境相关浓度亚砷酸盐的抗性。ArsD是一种同型二聚体，每个亚基中有三对相邻的半胱氨酸，即Cys12 - Cys13、Cys112 - Cys113和Cys119 - Cys120。每对相邻半胱氨酸结合一个As(III)或Sb(III)。用丙氨酸分别替代Cys112、Cys113、Cys119或Cys120，或成对替代，或缺失相邻半胱氨酸对的ArsD突变体，仍保留与ArsA相互作用、激活其ATP酶活性的能力。表达这些突变体的细胞保留了ArsD增强的As(III)外排和抗性。相比之下，分别或成对替代保守半胱氨酸Cys12、Cys13或Cys18的突变体无法激活ArsA或增强ArsAB泵的活性。有人提出，将As(III)传递至ArsAB泵并激活该泵需要ArsD的Cys12、Cys13和Cys18残基，而不是Cys112、Cys113、Cys119或Cys120残基。
