title: Arsenic Demethylation by a C·As Lyase in Cyanobacterium Nostoc sp. PCC 7120.
abstract: Arsenic, a ubiquitous toxic substance, exists mainly as inorganic forms in the environment. It is perceived that organoarsenicals can be demethylated and degraded into inorganic arsenic by microorganisms. Few studies have focused on the mechanism of arsenic demethylation in bacteria. Here, we investigated arsenic demethylation in a typical freshwater cyanobacterium Nostoc sp. PCC 7120. This bacterium was able to demethylate monomethylarsenite [MAs(III)] rapidly to arsenite [As(III)] and also had the ability to demethylate monomethylarsenate [MAs(V)] to As(III). The NsarsI encoding a C·As lyase responsible for MAs(III) demethylation was cloned from Nostoc sp. PCC 7120 and heterologously expressed in an As-hypersensitive strain Escherichia coli AW3110 (ΔarsRBC). Expression of NsarsI was shown to confer MAs(III) resistance through arsenic demethylation. The purified NsArsI was further identified and functionally characterized in vitro. NsArsI existed mainly as the trimeric state, and the kinetic data were well-fit to the Hill equation with K0.5 = 7.55 ± 0.33 μM for MAs(III), Vmax = 0.79 ± 0.02 μM min(-1), and h = 2.7. Both of the NsArsI truncated derivatives lacking the C-terminal 10 residues (ArsI10) or 23 residues (ArsI23) had a reduced ability of MAs(III) demethylation. These results provide new insights for understanding the important role of cyanobacteria in arsenic biogeochemical cycling in the environment.
authors.affiliation: Key Lab of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences , Xiamen 361021, People's Republic of China.|University of Chinese Academy of Sciences , Beijing 100049, People's Republic of China.
authors.forename: Yu
authors.initials: Y
authors.lastname: Yan
authors.affiliation: Key Lab of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences , Xiamen 361021, People's Republic of China.
authors.forename: Jun
authors.initials: J
authors.lastname: Ye
authors.affiliation: Key Lab of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences , Xiamen 361021, People's Republic of China.
authors.forename: Xi-Mei
authors.initials: XM
authors.lastname: Xue
authors.affiliation: Key Lab of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences , Xiamen 361021, People's Republic of China.|State Key Lab of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences , Beijing 100085, People's Republic of China.
authors.forename: Yong-Guan
authors.initials: YG
authors.lastname: Zhu
mesh_terms: D001151:Arsenic / Q000378:metabolism*; D018053:Arsenites / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000378:metabolism; D008190:Lyases / Q000378:metabolism*; D008745:Methylation; D046937:Nostoc / Q000235:genetics / Q000378:metabolism*; D055503:Protein Multimerization
chemical_list: D018053:Arsenites; D001426:Bacterial Proteins; D008190:Lyases; C015001:arsenite; D001151:Arsenic