Mechanistic Explanation of the Weak Carbonic Anhydrase's Esterase Activity

Microbially induced calcium carbonate precipitation through CO2 sequestration via an engineered Bacillus subtilis

BACKGROUND

Microbially induced calcium carbonate precipitation has been extensively researched for geoengineering applications as well as diverse uses within the built environment. Bacteria play a crucial role in producing calcium carbonate minerals, via enzymes including carbonic anhydrase-an enzyme with the capability to hydrolyse CO2, commonly employed in carbon capture systems. This study describes previously uncharacterised carbonic anhydrase enzyme sequences capable of sequestering CO2 and subsequentially generating CaCO3 biominerals and suggests a route to produce carbon negative cementitious materials for the construction industry.

RESULTS

Here, Bacillus subtilis was engineered to recombinantly express previously uncharacterised carbonic anhydrase enzymes from Bacillus megaterium and used as a whole cell catalyst allowing this novel bacterium to sequester CO2 and convert it to calcium carbonate. A significant decrease in CO2 was observed from 3800 PPM to 820 PPM upon induction of carbonic anhydrase and minerals recovered from these experiments were identified as calcite and vaterite using X-ray diffraction. Further experiments mixed the use of this enzyme (as a cell free extract) with Sporosarcina pasteurii to increase mineral production whilst maintaining a comparable level of CO2 sequestration.

CONCLUSION

Recombinantly produced carbonic anhydrase successfully sequestered CO2 and converted it into calcium carbonate minerals using an engineered microbial system. Through this approach, a process to manufacture cementitious materials with carbon sequestration ability could be developed.

The hydrolysis of indoxyl acetate: A versatile reaction to assay carbonic anhydrase activity by high-throughput screening

The interest in CO₂ capture and conversion by biological methodologies into various beneficial products is increased. In nature, there are enzymes, with hydration activity, which catalyze the reversible hydration of the CO₂ molecule and, thus, are of high interest for biotechnological applications. Such enzymes are carbonic anhydrases (CAs). Structural, functional and mutational studies have shown, that besides hydratase activity, CAs have exposed hydrolytic, particularly esterase activity, and importantly, both activities follow similar catalytic mechanisms in the same catalytic pocket. CAs activity measurement methods based on electrometric assays for hydration activity and nitrophenyl based esters for hydrolytic activity assays do not fulfill the requirements amenable for enzyme activity screening methods. By this study, we were aiming to develop an indigogenic assay method based on the esterase activity of CAs. The first time use of indoxyl acetate as a substrate for CA has shown promising results to gain simplicity, repeatability, and applicability to implement high-throughput screening methods.

Structure and mechanism of copper-carbonic anhydrase II: a nitrite reductase

Nitric oxide (NO) promotes vasodilation through the activation of guanylate cyclase, resulting in the relaxation of the smooth muscle vasculature and a subsequent decrease in blood pressure. Therefore, its regulation is of interest for the treatment and prevention of heart disease. An example is pulmonary hypertension which is treated by targeting this NO/vasodilation pathway. In bacteria, plants and fungi, nitrite (NO2 -) is utilized as a source of NO through enzymes known as nitrite reductases. These enzymes reduce NO2 - to NO through a catalytic metal ion, often copper. Recently, several studies have shown nitrite reductase activity of mammalian carbonic anhydrase II (CAII), yet the molecular basis for this activity is unknown. Here we report the crystal structure of copper-bound human CAII (Cu-CAII) in complex with NO2 - at 1.2 Å resolution. The structure exhibits Type 1 (T-1) and 2 (T-2) copper centers, analogous to bacterial nitrite reductases, both required for catalysis. The copper-substituted CAII active site is penta-coordinated with a 'side-on' bound NO2 -, resembling a T-2 center. At the N terminus, several residues that are normally disordered form a porphyrin ring-like configuration surrounding a second copper, acting as a T-1 center. A structural comparison with both apo- (without metal) and zinc-bound CAII (Zn-CAII) provides a mechanistic picture of how, in the presence of copper, CAII, with minimal conformational changes, can function as a nitrite reductase.

Why hydroxy-proline improves the catalytic power of the peptidoglycan N-deacetylase enzyme: insight from theory

Nature exploits different strategies for enhancing the catalytic activity of enzymes, often resorting to producing beneficial mutations. The case of post-translational proline hydroxylation mutation in the active site of polysaccharide deacetylase (PDA) Bc1960 from Bacillus cereus is an interesting example of how small chemical modifications can cause significant improvements in enzymatic activity. In the present study the deacetylation mechanism promoted by both OH-proline (2Hyp) and standard proline (Pro) containing PDA is investigated using density functional theory. Although the mechanism presented for the two examined enzymes is in agreement with protease catalysis in metalloenzymes, the analysis along the potential energy surface (PES) reveals that the intermediate and product benefit energetically from the presence of the hydroxyl group on the proline. Our calculations provide evidence that for PDA-2Hyp, the hydrogen bond network established by the -OH group on the Cα of the proline with its closest neighbors stabilizes the transition states and, consequently, the reaction takes advantage of this. These results further contribute towards explaining the different catalytic activity experimentally observed for the polysaccharide deacetylase enzymes.