Functional adaptation of mercuric reductases from the deep brine environment of Atlantis II in the Red Sea to high temperature
July 16-20, 2017
The lower convective layer (LCL) of the Atlantis II (ATII) brine pool of the red sea is a unique environment characterized by high salinity of around 4 Molar, temperature of 68οC, and very high concentrations of heavy metals. We have previously described a metagenome-derived mercuric reductase, ATII-LCL MerA, from the LCL of the ATII brine pool that is thermo-stable at 60oC and retain more than 70% of its activity after 10 minutes incubation at 70oC. One of the structural characteristics of this enzyme, that distinguish it from a thermo-sensitive ortholog, is the limited substitutions of amino acids, less than 9%, including the presence of 4 aspartic acids at positions 414 to 417 replacing 4 alanine in the thermo-sensitive MerA. In this work, we identified a metagenome-derived MerA from the ATII-LCL environment, ATII-LCL-NH, that is lacking all the substitutions observed in ATII-LCL MerA. Site-directed mutagenesis replacing alanine 415 and 416 found in ATII-LCL-NH with the corresponding aspartic acids present in ATII-LCL increased the thermo-stability of the enzyme. However, substituting the 4 alanine, 415 to 417, with the corresponding four aspartic acids present in ATII-LCL decreased tremendously the thermal stability of the enzyme. Three-dimensional modeling of the MerA with the substituted Aspartic acids 415/416 revealed newly formed salt-bridge with arginine residue at position 420 and hydrogen bonds that may explain the enhanced thermal stability of this ATII-LCL-NH with the substituted Aspartic 415/416.
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Mohamad Maged and Hamza El dorry, "Functional adaptation of mercuric reductases from the deep brine environment of Atlantis II in the Red Sea to high temperature" in "Biochemical and Molecular Engineering XX", Wilfred Chen, University of Delaware, USA Nicole Borth, Universität für Bodenkultur, Vienna, Austria Stefanos Grammatikos, UCB Pharma, Belgium Eds, ECI Symposium Series, (2017). http://dc.engconfintl.org/biochem_xx/22