Crystallization, characterization and preliminary X-ray crystallographic analysis of GK2848, a putative carbonic anhydrase of Geobacillus kaustophilus

Structural and functional characterization of a putative carbonic anhydrase from Geobacillus kaustophilus reveals its cambialistic function

Carbonic anhydrases (CA) are the most ubiquitous ancient zinc metalloenzymes known. Here we report the structural and functional analysis of a hypothetical protein GK2848 from Geobacillus kaustophilus. The analysis revealed that it belongs to the γ-class of CA (termed as Cag). Only a limited number of γ-class CA's have been characterized till date. Interestingly Cag contains magnesium at its active site instead of a traditional zinc ion. Based on the structural and sequence comparison with similar γ-CA's the putative active site residues of Cag were identified. This analysis revealed that an important catalytic residue and a proton shuttle residue (Glu62 and Glu84 respectively) of Cam (previously characterized γ-CA from Methanosarcina thermophila) are absent in Cag, however certain other active site residues are conserved both in Cag and Cam. This suggests that Cag uses a different set of residues for the reversible hydration of CO₂ to HCO₃^- when compared with Cam. Inductively Coupled Plasma - Optical Emission Spectrometry (ICP-OES) and ²⁵Mg and ⁶⁷Zn NMR studies on Cag and its mutants revealed that either Mg or Zn can occupy the active site which suggests the cambialistic nature of the enzyme.

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

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.

Functional characterization and molecular modelling of FnFgBP, a surface protein from Streptococcus agalactiae

GBS1263 (FnFgBP) exhibits dual-ligand (fibronectin and fibrinogen) binding property. Molecular modeling of FnFgBP is suggestive of a unique ligand binding mechanism.

Prokaryotic carbonic anhydrases of Earth's environment

Carbonic anhydrase is a metalloenzyme catalyzing the reversible hydration of carbon dioxide to bicarbonate. Five independently evolved classes have been described for which one or more are found in nearly every cell type underscoring the general importance of this ubiquitous enzyme in Nature. The bulk of research to date has centered on the enzymes from mammals and plants with less emphasis on prokaryotes. Prokaryotic carbonic anhydrases play important roles in the ecology of Earth's biosphere including acquisition of CO2 for photosynthesis and the physiology of aerobic and anaerobic prokaryotes decomposing the photosynthate back to CO2 thereby closing the global carbon cycle. This review focuses on the physiology and biochemistry of carbonic anhydrases from prokaryotes belonging to the domains Bacteria and Archaea that play key roles in the ecology of Earth's biosphere.