title: A novel mercuric reductase from the unique deep brine environment of Atlantis II in the Red Sea.
abstract: A unique combination of physicochemical conditions prevails in the lower convective layer (LCL) of the brine pool at Atlantis II (ATII) Deep in the Red Sea. With a maximum depth of over 2000 m, the pool is characterized by acidic pH (5.3), high temperature (68 °C), salinity (26%), low light levels, anoxia, and high concentrations of heavy metals. We have established a metagenomic dataset derived from the microbial community in the LCL, and here we describe a gene for a novel mercuric reductase, a key component of the bacterial detoxification system for mercuric and organomercurial species. The metagenome-derived gene and an ortholog from an uncultured soil bacterium were synthesized and expressed in Escherichia coli. The properties of their products show that, in contrast to the soil enzyme, the ATII-LCL mercuric reductase is functional in high salt, stable at high temperatures, resistant to high concentrations of Hg(2+), and efficiently detoxifies Hg(2+) in vivo. Interestingly, despite the marked functional differences between the orthologs, their amino acid sequences differ by less than 10%. Site-directed mutagenesis and kinetic analysis of the mutant enzymes, in conjunction with three-dimensional modeling, have identified distinct structural features that contribute to extreme halophilicity, thermostability, and high detoxification capacity, suggesting that these were acquired independently during the evolution of this enzyme. Thus, our work provides fundamental structural insights into a novel protein that has undergone multiple biochemical and biophysical adaptations to promote the survival of microorganisms that reside in the extremely demanding environment of the ATII-LCL.
authors.affiliation: From the Department of Biology and the Science and Technology Research Center, School of Sciences and Engineering, The American University in Cairo, AUC Avenue, P. O. Box 74, New Cairo 11835, Egypt.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Sayed
authors.forename: Mohamed A
authors.initials: MA
authors.lastname: Ghazy
authors.forename: Ari J S
authors.initials: AJ
authors.lastname: Ferreira
authors.forename: João C
authors.initials: JC
authors.lastname: Setubal
authors.forename: Felipe S
authors.initials: FS
authors.lastname: Chambergo
authors.forename: Amged
authors.initials: A
authors.lastname: Ouf
authors.forename: Mustafa
authors.initials: M
authors.lastname: Adel
authors.forename: Adam S
authors.initials: AS
authors.lastname: Dawe
authors.forename: John A C
authors.initials: JA
authors.lastname: Archer
authors.forename: Vladimir B
authors.initials: VB
authors.lastname: Bajic
authors.forename: Rania
authors.initials: R
authors.lastname: Siam
authors.forename: Hamza
authors.initials: H
authors.lastname: El-Dorry
mesh_terms: D001483:Base Sequence; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008628:Mercury / Q000737:chemistry* / Q000378:metabolism; D054892:Metagenome; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009792:Oceans and Seas; D010088:Oxidoreductases / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012623:Seawater / Q000382:microbiology*; D014871:Water Microbiology
chemical_list: D011994:Recombinant Proteins; D010088:Oxidoreductases; C021551:mercuric reductase; D008628:Mercury
keywords: Atlantis II Brine Pool; Enzyme Kinetics; Enzyme Mechanisms; Enzyme Structure; Extreme Halophilic; Mercuric Reductase; Metagenomics; Mutagenesis Site-specific; Red Sea Atlantis II; Thermophilic