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Looking toward the Rim of the Active Site Cavity of Druggable Human Carbonic Anhydrase Isoforms.

ABSTRACT: We report the synthesis and biochemical evaluation of a series of substituted 4-(4-aroylpiperazine-1-carbonyl)benzenesulfonamides (5a-s) developed as inhibitors of druggable carbonic anhydrase (CA) isoforms, as tools for the identification of new therapeutics. X-ray crystallography confirmed that this class of benzenesulfonamides binds CAs through the canonical anchoring of the benzenesulfonamide moiety to the metal ion and a tail-mediated recognition of the middle/top area of the active site cavity. Compound 5e (R = 2-Cl) demonstrated relevant selectivity toward brain-expressed hCA VII. The best balancing in binding affinity and selectivity toward tumor-expressed hCA IX/hCA XII over ubiquitous hCA I/hCA II was found for inhibitor 5o (R = 3-NO₂). Notably 5b (R = 2-F) proved to be the most efficacious inhibitor of hCA XII for which computational studies elucidated the CA recognition process.

SUBMITTER: Mancuso F

PROVIDER: S-EPMC7236538 | biostudies-literature |

REPOSITORIES: biostudies-literature

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New Dihydrothiazole Benzensulfonamides: Looking for Selectivity toward Carbonic Anhydrase Isoforms I, II, IX, and XII.

Project description:In the present study we investigated the structure-activity relationships of a new series of 4-[(3-ethyl-4-aryl-2,3-dihydro-1,3-thiazol-2-ylidene)amino]benzene-1-sulfonamides (EMAC10101a-m). All synthesized compounds, with the exception of compound EMAC10101k, preferentially inhibit off-target hCA II isoform. Within the series, compound EMAC10101d, bearing a 2,4-dichorophenyl substituent in position 4 of the dihydrothiazole ring, was the most potent and selective toward hCA II with an inhibitory activity in the low nanomolar range.

| S-EPMC7236253 | biostudies-literature

<i>N</i>-Acylbenzenesulfonamide Dihydro-1,3,4-oxadiazole Hybrids: Seeking Selectivity toward Carbonic Anhydrase Isoforms.

Project description:A series of N-acylbenzenesulfonamide dihydro-1,3,4-oxadiazole hybrids (EMAC8000a-m) was designed and synthesized with the aim to target tumor associated carbonic anhydrase (hCA) isoforms IX and XII. Most of the compounds were selective inhibitors of the tumor associated hCA XII. Moreover, resolution of EMAC8000d racemic mixture led to the isolation of the levorotatory eutomer exhibiting an increase of hCA XII inhibition potency and selectivity with respect to hCA II. Computational studies corroborated these data. Overall our data indicate that both substitution pattern and stereochemistry of dihydro-1,3,4-oxadiazole could be considered as key factors to determine activity and selectivity toward hCA isozymes. These results can provide further indication for the design and optimization of selective hCA inhibitors.

| S-EPMC5554910 | biostudies-literature

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

Project description: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 ?-carbonic anhydrase (?-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 ?-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 ?-CA enzyme, we created a library of variants around the active site residues and successfully improved the enzyme activity by 17-fold. As several ?-CAs have been reported without measurable activity, this provides further clues as to critical residues. Our study reveals insights into the halophilic ?-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.

| S-EPMC7199487 | biostudies-literature

Cancer Drug Development of Carbonic Anhydrase Inhibitors beyond the Active Site.

Project description:Carbonic anhydrases (CAs) catalyze the reversible hydration of carbon dioxide to produce bicarbonate and a proton. Multiple CA isoforms are implicated in a range of diseases, including cancer. In solid tumors, continuously dividing cells create hypoxic conditions that eventually lead to an acidic microenvironment. Hypoxic tumor cells have different mechanisms in place to regulate and adjust the surrounding microenvironment for survival. These mechanisms include expression of CA isoform IX (CA IX) and XII (CA XII). These enzymes help maintain a physiological intracellular pH while simultaneously contributing to an acidic extracellular pH, leading to tumor cell survival. Expression of CA IX and CA XII has also been shown to promote tumor cell invasion and metastasis. This review discusses the characteristics of CA IX and CA XII, their mechanism of action, and validates their prospective use as anticancer targets. We discuss the current status of small inhibitors that target these isoforms, both classical and non-classical, and their future design in order to obtain isoform-specificity for CA IX and CA XII. Biologics, such as monoclonal antibodies, monoclonal-radionuclide conjugated chimeric antibodies, and antibody-small molecule conjugates are also discussed.

| S-EPMC6099549 | biostudies-literature

Active-site solvent replenishment observed during human carbonic anhydrase II catalysis.

Project description:Human carbonic anhydrase II (hCA II) is a zinc metalloenzyme that catalyzes the reversible hydration/dehydration of CO2/HCO3-. Although hCA II has been extensively studied to investigate the proton-transfer process that occurs in the active site, its underlying mechanism is still not fully understood. Here, ultrahigh-resolution crystallographic structures of hCA II cryocooled under CO2 pressures of 7.0 and 2.5 atm are presented. The structures reveal new intermediate solvent states of hCA II that provide crystallographic snapshots during the restoration of the proton-transfer water network in the active site. Specifically, a new intermediate water (WI') is observed next to the previously observed intermediate water WI, and they are both stabilized by the five water molecules at the entrance to the active site (the entrance conduit). Based on these structures, a water network-restructuring mechanism is proposed, which takes place at the active site after the nucleophilic attack of OH- on CO2. This mechanism explains how the zinc-bound water (WZn) and W1 are replenished, which are directly responsible for the reconnection of the His64-mediated proton-transfer water network. This study provides the first 'physical' glimpse of how a water reservoir flows into the hCA II active site during its catalytic activity.

| S-EPMC5755581 | biostudies-literature

Entrapment of carbon dioxide in the active site of carbonic anhydrase II.

Project description:The visualization at near atomic resolution of transient substrates in the active site of enzymes is fundamental to fully understanding their mechanism of action. Here we show the application of using CO(2)-pressurized, cryo-cooled crystals to capture the first step of CO(2) hydration catalyzed by the zinc-metalloenzyme human carbonic anhydrase II, the binding of substrate CO(2), for both the holo and the apo (without zinc) enzyme to 1.1A resolution. Until now, the feasibility of such a study was thought to be technically too challenging because of the low solubility of CO(2) and the fast turnover to bicarbonate by the enzyme (Liang, J. Y., and Lipscomb, W. N. (1990) Proc. Natl. Acad. Sci. U. S. A. 87, 3675-3679). These structures provide insight into the long hypothesized binding of CO(2) in a hydrophobic pocket at the active site and demonstrate that the zinc does not play a critical role in the binding or orientation of CO(2). This method may also have a much broader implication for the study of other enzymes for which CO(2) is a substrate or product and for the capturing of transient substrates and revealing hydrophobic pockets in proteins.

| S-EPMC2576554 | biostudies-literature

Structure and catalysis by carbonic anhydrase II: role of active-site tryptophan 5.

Project description:The tryptophan residue Trp5, highly conserved in the ? class of carbonic anhydrases including human carbonic anhydrase II (HCA II), is positioned at the entrance of the active site cavity and forms a ?-stacking interaction with the imidazole ring of the proton shuttle His64 in its outward orientation. We have observed that replacement of Trp5 in HCA II caused significant structural changes, as determined by X-ray diffraction, in the conformation of 11 residues at the N-terminus and in the orientation of the proton shuttle residue His64. Most significantly, two variants W5H and W5E HCA II had His64 predominantly outward in orientation, while W5F and wild type showed the superposition of both outward and inward orientations in crystal structures. Although Trp5 influences the orientation of the proton shuttle His64, this orientation had no significant effect on the rate constant for proton transfer near 1?s(-1), determined by exchange of (18)O between CO(2) and water measured by mass spectrometry. The apparent values of the pK(a) of the zinc-bound water and the proton shuttle residue suggest that different active-site conformations influence the two stages of catalysis, the proton transfer stage and the interconversion of CO(2) and bicarbonate.

| S-EPMC3223279 | biostudies-literature

A short, strong hydrogen bond in the active site of human carbonic anhydrase II.

Project description:The crystal structure of human carbonic anhydrase II (HCA II) obtained at 0.9 A resolution reveals that a water molecule, termed deep water, Dw, and bound in a hydrophobic pocket of the active site forms a short, strong hydrogen bond with the zinc-bound solvent molecule, a conclusion based on the observed oxygen-oxygen distance of 2.45 A. This water structure has similarities with hydrated hydroxide found in crystals of certain inorganic complexes. The energy required to displace Dw contributes in significant part to the weak binding of CO(2) in the enzyme-substrate complex, a weak binding that enhances k(cat) for the conversion of CO(2) into bicarbonate. In addition, this short, strong hydrogen bond is expected to contribute to the low pK(a) of the zinc-bound water and to promote proton transfer in catalysis.

| S-EPMC2810610 | biostudies-literature

Glycomimetic Based Approach toward Selective Carbonic Anhydrase Inhibitors.

Project description:The synthesis of selective inhibitors of human carbonic anhydrases (hCAs) is of paramount importance to avoid side effects derived from undesired interactions with isoforms not involved in the targeted pathology, and this was partially addressed with the introduction of a sugar moiety (the so-called "sugar approach"). Since glycomimetics are considered more selective than the parent sugars in inhibiting carbohydrate-processing enzyme, we explored the possibility of further tuning the selectivity of hCAs inhibitors by combining the sulfonamide moiety with a sugar analogue residue. In particular, we report the synthesis of two novel hCAs inhibitors 2 and 3 which feature the presence of a piperidine iminosugar and an additional carbohydrate moiety derived from levoglucosenone (1), a key intermediate derived from cellulose pyrolysis. Biological assays revealed that iminosugar 2 is a very strong inhibitor of the central nervous system (CNS) abundantly expressed hCA VII (K I of 7.4 nM) and showed a remarkable selectivity profile toward this isoform. Interestingly, the presence of levoglucosenone in glycomimetic 3 imparted a strong inhibitory activity toward the tumor associated hCA IX (K I of 35.9 nM).

| S-EPMC7236246 | biostudies-literature

The active site architecture of Pisum sativum beta-carbonic anhydrase is a mirror image of that of alpha-carbonic anhydrases.

Project description:We have determined the structure of the beta-carbonic anhydrase from the dicotyledonous plant Pisum sativum at 1.93 A resolution, using a combination of multiple anomalous scattering off the active site zinc ion and non-crystallographic symmetry averaging. The mol- ecule assembles as an octamer with a novel dimer of dimers of dimers arrangement. Two distinct patterns of conservation of active site residues are observed, implying two potentially mechanistically distinct classes of beta-carbonic anhydrases. The active site is located at the interface between two monomers, with Cys160, His220 and Cys223 binding the catalytic zinc ion and residues Asp162 (oriented by Arg164), Gly224, Gln151, Val184, Phe179 and Tyr205 interacting with the substrate analogue, acetic acid. The substrate binding groups have a one to one correspondence with the functional groups in the alpha-carbonic anhydrase active site, with the corresponding residues being closely superimposable by a mirror plane. Therefore, despite differing folds, alpha- and beta-carbonic anhydrase have converged upon a very similar active site design and are likely to share a common mechanism.

| S-EPMC310211 | biostudies-literature

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