Frontiers in Microbiology (Apr 2020)

Crystal Structure and Active Site Engineering of a Halophilic γ-Carbonic Anhydrase

  • Malvina Vogler,
  • Malvina Vogler,
  • Ram Karan,
  • Dominik Renn,
  • Alexandra Vancea,
  • Marie-Theres Vielberg,
  • Stefan W. Grötzinger,
  • Priya DasSarma,
  • Shiladitya DasSarma,
  • Jörg Eppinger,
  • Michael Groll,
  • Magnus Rueping

DOI
https://doi.org/10.3389/fmicb.2020.00742
Journal volume & issue
Vol. 11

Abstract

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Environments previously thought to be uninhabitable offer a tremendous wealth of unexplored microorganisms and enzymes. In this paper, we present the discovery and characterization of a novel γ-carbonic anhydrase (γ-CA) from the polyextreme Red Sea brine pool Discovery Deep (2141 m depth, 44.8°C, 26.2% salt) by single-cell genome sequencing. The extensive analysis of the selected gene helps demonstrate the potential of this culture-independent method. The enzyme was expressed in the bioengineered haloarchaeon Halobacterium sp. NRC-1 and characterized by X-ray crystallography and mutagenesis. The 2.6 Å crystal structure of the protein shows a trimeric arrangement. Within the γ-CA, several possible structural determinants responsible for the enzyme’s salt stability could be highlighted. Moreover, the amino acid composition on the protein surface and the intra- and intermolecular interactions within the protein differ significantly from those of its close homologs. To gain further insights into the catalytic residues of the γ-CA enzyme, we created a library of variants around the active site residues and successfully improved the enzyme activity by 17-fold. As several γ-CAs have been reported without measurable activity, this provides further clues as to critical residues. Our study reveals insights into the halophilic γ-CA activity and its unique adaptations. The study of the polyextremophilic carbonic anhydrase provides a basis for outlining insights into strategies for salt adaptation, yielding enzymes with industrially valuable properties, and the underlying mechanisms of protein evolution.

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