Browsing by Author "Ramadan E."

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    Molecular adaptations of bacterial mercuric reductase to the hypersaline Kebrit Deep in the Red Sea
    (American Society for Microbiology, 2019) Ramadan E.; Maged M.; Hosseiny A.E.; Chambergo F.S.; Setubal J.C.; Dorry H.E.; Department of Biology; School of Sciences and Engineering; The American University in Cairo; New Cairo; Egypt; Escola de Artes Ci�ncias e Humanidades; Universidade de S�o Paulo; S�o Paulo; Brazil; Instituto de Qu�mica; Universidade de S�o Paulo; S�o Paulo; Brazil; Faculty of Pharmacy; Department of Pharmacology and Biochemistry; The British University in Egypt; El-Sherouk City; Egypt; Faculty of Biotechnology; October University for Modern Sciences and Arts; Cairo; Egypt
    The hypersaline Kebrit Deep brine pool in the Red Sea is characterized by high levels of toxic heavy metals. Here, we describe two structurally related mercuric reductases (MerAs) from this site which were expressed in Escherichia coli. Sequence similarities suggest that both genes are derived from proteobacteria, most likely the Betaproteobacteria or Gammaproteobacteria. We show that one of the enzymes (K35NH) is strongly inhibited by NaCl, while the other (K09H) is activated in a NaCl-dependent manner. We infer from this difference that the two forms might support the detoxification of mercury in bacterial microorganisms that employ the compatible solutes and salt-in strategies, respectively. Three-dimensional structure modeling shows that all amino acid substitutions unique to each type are located outside the domain responsible for formation of the active MerA homodimer, and the vast majority of these are found on the surface of the molecule. Moreover, K09H exhibits the predominance of acidic over hydrophobic side chains that is typical of halophilic salt-dependent proteins. These findings enhance our understanding of how selection pressures imposed by two environmental stressors have endowed MerA enzymes with catalytic properties that can potentially function in microorganisms that utilize distinct mechanisms for osmotic balance in hypersaline environments. � 2019 American Society for Microbiology. All Rights Reserved.
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    Thermal stability of a mercuric reductase from the Red Sea Atlantis II hot brine environment as analyzed by site-directed mutagenesis
    (American Society for Microbiology, 2019) Maged M.; Hosseiny A.E.; Saadeldin M.K.; Aziz R.K.; Ramadan E.; Department of Biology; School of Sciences and Engineering; The American University in Cairo; New Cairo; Egypt; Department of Microbiology and Immunology; Faculty of Pharmacy; Cairo University; Cairo; Egypt; Faculty of Pharmacy; The British University in Egypt (BUE); El Shorouk; Egypt; Science and Technology Research Center; School of Sciences and Engineering; The American University in Cairo; New Cairo; Egypt; Faculty of Biotechnology; October University for Modern Sciences and Arts; 6th October City; Cairo; Egypt
    The lower convective layer (LCL) of the Atlantis II brine pool of the Red Sea is a unique environment in terms of high salinity, temperature, and high concentrations of heavy metals. Mercuric reductase enzymes functional in such extreme conditions could be considered a potential tool in the environmental detoxification of mercurial poisoning and might alleviate ecological hazards in the mining industry. Here, we constructed a mercuric reductase library from Atlantis II, from which we identified genes encoding two thermostable mercuric reductase (MerA) isoforms: one is halophilic (designated ATII-LCL) while the other is not (designated ATII-LCLNH). The ATII-LCL MerA has a short motif composed of four aspartic acids (4D414- 417) and two characteristic signature boxes that played a crucial role in its thermal stability. To further understand the mechanism behind the thermostability of the two studied enzymes, we mutated the isoform ATII-LCL-NH and found that the substitution of 2 aspartic acids (2D) at positions 415 and 416 enhanced the thermal stability, while other mutations had the opposite effect. The 2D mutant showed superior thermal tolerance, as it retained 81% of its activity after 10 min of incubation at 70�C. A three-dimensional structure prediction revealed newly formed salt bridges and H bonds in the 2D mutant compared to the parent molecule. To the best of our knowledge, this study is the first to rationally design a mercuric reductase with enhanced thermal stability, which we propose to have a strong potential in the bioremediation of mercurial poisoning. � 2019 American Society for Microbiology.