Identification and expression of cotton (Gossypium hirsutum L.) plastidial carbonic anhydrase

Four carbonic anhydrase (CA) cDNA clones were isolated from a 48 h dark-grown cotton (Gossypium hirsutum L.) seedling cDNA library. Nucleotide sequence analysis revealed two different CA isoforms designated GhCA1 and GhCA2. The encoded polypeptides possess N-terminal serine/threonine-rich regions indicative of plastid transit peptides, and approximately 80% sequence identity to other plant plastidial beta-CAs. The GhCA1 cDNA encodes a nearly complete preprotein of 323 amino acids with a molecular mass of 34.9 kDa and a predicted mature protein of 224 amino acids with a molecular mass of 24.3 kDa. Eleven nucleotide differences within ORFs of GhCA1 and GhCA2 result in 5 conservative amino acid substitutions. The 3' GhCA2 untranslated region contains five additional substitutions and one single nucleotide addition. GhCA1 clones, nearly full-length or with 70% of the transit peptide deleted, were expressed as LacZ alpha fusion proteins in E. coli. Lysates of these strains contained 9-fold higher levels of CA activity as compared to untransformed controls and this activity was inhibited by CA-specific inhibitors. Sulfanilamide, acetazolamide, ethoxyzolamide, each at 10 mM, inhibited recombinant CA activity approximately 50%, 65%, and 75%, respectively. In plant tissue homogenates these inhibitors reduced CA activity by 50%, 70%, and 95%, respectively. Although CA activity was bighest in extracts of mature cotton leaves, probing total RNA with GhCA1 revealed CA transcript levels to be highest in the cotyledons of dark-grown cotton seedlings. Collectively, our data indicate the presence of a plastid-localized CA in cotyledons of germinated seeds, suggesting a role for CA in postgerminative growth.

Localization of carbonic anhydrase in guinea pig Bowman's glands

We examined the histochemical localization of carbonic anhydrase (CA) in Bowman's glands by light and electron microscopy. Neither CAI nor CAII was detected immunohistochemically in the duct cells. However, by enzyme histochemistry the duct cells revealed electron-dense precipitates demonstrative of CA in the microvilli and intercellular digitations. The reaction product was also noted in small vesicles in the cytoplasm of duct cells. In cells of the acini, the well-developed short microvilli, basolateral cell membrane, and mitochondria along the basolateral membrane showed strong deposits indicating CA activity. Dense reaction product of CA was also detected in a small core within the electron-lucent granules of the secretory cells, although CAI and CAII were not detected by immunostaining in the secretory granules. Although the functional significance of CA in Bowman's glands is obscure, the enzyme may play a role in regulation of pH and ion balance in the mucous layer covering the olfactory epithelium. The presence of CA activity in the ducts suggests that these structures are not simple tubes serving as a conduit for secretory substances but participate in modifying the luminal content by secreting CA. (J Histochem Cytochem 47:1525-1531, 1999)

Complementary role of two fragments of domain V of 23 S ribosomal RNA in protein folding

We have shown that the domain V of bacterial 23 S rRNA could fold denatured proteins to their active state. This segment of 23 S rRNA could further be split into two parts. One part containing mainly the central loop of domain V could bind denatured human carbonic anhydrase I stably. This association could be reversed by adding the other part of domain V. The released enzyme was directed in such a way by the central loop of domain V that it could now fold by itself to active form. This agrees with our earlier observation that proteins fold within the cell posttranslationally, a process that is completed after release of the newly synthesized polypeptide from the ribosome (Chattopadhyay, S., Pal, S., Chandra, S., Sarkar, D., and DasGupta, C. (1999) Biochim. Biophys. Acta 1429, 293-298).

Changes in protein expression in the vestibular nuclei during vestibular compensation

In the guinea pig, labyrinthectomy induces an immediate depression of the resting discharges in the neurons of the ipsilateral vestibular nuclei. Later on, in spite of the persistent deprivation of their ipsilateral labyrinthine input, a spontaneous restoration of activity, which is complete within 1 week, occurs in these neurons. Here, by using computer-assisted quantitative two-dimensional gel analysis, we have detected three proteins whose expressions were increased in the ipsilateral vestibular nuclei 1 week after unilateral labyrinthectomy. The spatio-temporal pattern of this phenomenon was compatible with a role for it in the restoration of activity in the vestibular neurons deprived of their ipsilateral labyrinthine input. Furthermore, the N-terminal amino acid sequences of two of these expressed proteins were obtained.

Models of F.H contacts relevant to the binding of fluoroaromatic inhibitors to carbonic anhydrase II

[formula: see text] Complexes formed between fluorobenzene and N-methylformamide or benzene have been used as models of the interaction of fluoroaromatic drugs with carbonic anhydrase II. These structures have been investigated via ab initio and density functional methods, including HF, B3LYP, and MP2 procedures. The results of the calculations are consistent with the hypothesis, suggested originally by experimental X-ray crystal structures of the drug-receptor complexes, that favorable fluorine-hydrogen interactions affect binding affinity.

Reduced activity of enzymes coupling ATP-generating with ATP-consuming processes in the failing myocardium

Coupling of ATP-generating with ATP-consuming processes is an essential component in the cardiac bioenergetics responsible for optimal myocardial function. Although a number of enzymatic systems have been implicated in securing proper intracellular energy communication, their integrative response in a failing myocardium has not been determined so far. Therefore, we measured catalytic activities of enzymes responsible for the communication between ATP-generating and ATP-consuming processes in ventricular samples obtained from normal dogs and dogs with tachycardia-induced heart failure. In the failing myocardium, phosphotransfer activities of creatine kinase, adenylate kinase, 3-phosphoglycerate kinase and pyruvate kinase, which collectively deliver ATP and remove ADP from myofibrillar ATPases, were depressed by 30, 21, 44 and 20%, respectively, when compared to normal controls. The activity of hexokinase, an enzyme which directs phosphoryls into the glycolytic phosphotransfer pathway, was unchanged. Also, the activity of glyceraldehyde-3-phosphate dehydrogenase, which may shuttle inorganic phosphate between ATPases and ATP-synthases, was not affected by heart failure. However, the CO2-hydration activity of carbonic anhydrase, which together with creatine kinase, is presumed responsible for removal of protons from ATPases, was diminished by 21%. As these enzymatic systems are collectively required for adequate delivery of high-energy phosphoryl to, and removal of end-products from, cellular ATPases, the cumulative deficit in their flux capacities may provide a bioenergetic basis for impaired contraction-relaxation in the failing heart.

Inhibition of intravacuolar acidification by antisense RNA decreases osteoclast differentiation and bone resorption in vitro

The role of proton transport and production in osteoclast differentiation was studied in vitro by inhibiting the transcription/translation of carbonic anhydrase II (CA II) and vacuolar H(+)-ATPase (V-ATPase) by antisense RNA molecules. Antisense RNAs targeted against CA II, or the 16 kDa or 60 kDa subunit of V-ATPase were used to block the expression of the specific proteins. A significant decrease in bone resorption rate and TRAP-positive osteoclast number was seen in rat bone marrow cultures and fetal mouse metacarpal cultures after antisense treatment. Intravacuolar acidification in rat bone marrow cells was also significantly decreased after antisense treatment. The CA II antisense RNA increased the number of TRAP-positive mononuclear cells, suggesting inhibition of osteoclast precursor fusion. Antisense molecules decreased the number of monocytes and macrophages, but increased the number of granulocytes in marrow cultures. GM-CSF, IL-3 and IL-6 were used to stimulate haematopoietic stem cell differentiation. The 16 kDa V-ATPase antisense RNA abolished the stimulatory effect of GM-CSF, IL-3 and IL-6 on TRAP-positive osteoclast formation, but did not affect the formation of monocytes and macrophages after IL-3 treatment, or the formation of granulocytes after IL-6 treatment. These results suggest that CA II and V-ATPase are needed, not only for the actual resorption, but also for osteoclast formation in vitro.

Identification of the zinc-binding protein specifically present in male rat liver as carbonic anhydrase III

A zinc (Zn)-binding protein that is present specifically in the livers of male adult rats was detected by HPLC with in-line detection by mass spectrometry (ICP MS). The Zn-binding protein was purified on Sephadex G-75 and G3000SW HPLC columns. and was identified as carbonic anhydrase III (CAIII) based on the amino acid sequence of a peptide obtained on lysyl endopeptidase digestion. CAIII is expressed as one of the major Zn-binding proteins in the livers of male rats in an age-dependent manner, a comparable amount of Zn to that of copper, Zn-superoxide dismutase (Cu,Zn-SOD) being bound to CAIII at 8 weeks of age. Castration at 4 or 8 weeks of age was shown to reduce Zn bound to CAIII to 47.5% of the sham-operated control level, suggesting that the sex-dependent expression of CAIII is partly regulated by a sex hormone, androgen. The concentration of CAIII in the livers of Long-Evans rats with a cinnamon-like coat color (LEC rats), an animal model of Wilson disease, was also estimated as Zn bound to CAIII and shown to be lower than that in Wistar rats before the onset of hepatitis. The concentration of CAIII was decreased specifically by repeated injections of cupric ions without the Cu,Zn-SOD concentration being affected.

Carbonic anhydrase inhibitors: synthesis of water-soluble, topically effective intraocular pressure lowering aromatic/heterocyclic sulfonamides containing 8-quinoline-sulfonyl moieties: is the tail more important than the ring?

Reaction of 20 aromatic/heterocyclic sulfonamides containing a free amino, imino, hydrazino or hydroxyl group, with 8-quinoline-sulfonyl chloride afforded a series of water-soluble (as hydrochloride or triflate salts) compounds. The new derivatives were assayed as inhibitors of the zinc enzyme carbonic anhydrase (CA), and more precisely of three of its isozymes, CA I, II (cytosolic forms) and IV (membrane-bound form), involved in important physiological processes. Efficient inhibition was observed against all three isozymes, but especially against CA II (in nanomolar range), which is the isozyme known to play a critical role in aqueous humor secretion within the ciliary processes of the eye. Some of the best inhibitors synthesized were topically applied as 2% water solutions onto the eye of normotensive and glaucomatous albino rabbits, when strong and long-lasting intraocular pressure (IOP) lowering was observed with many of them. This result prompted us to reanalyze the synthetic work done by other groups for the design of water soluble, topically effective antiglaucoma sulfonamides. According to these researchers, the IOP lowering effect is due to the intrinsic nature of the specific heterocyclic sulfonamide considered, among which the thienothiopyran-2-sulfonamide derivatives represent the best studied case. Indeed, the first agents developed for such applications, such as dorzolamide, are derivatives of this ring system. In order to prove that the tail (in this case the 8-quinoline-sulfonyl moiety) conferring water solubility to a sulfonamide CA inhibitor is more important than the ring to which the sulfonamido group is grafted, we also prepared a dorzolamide derivative to which the 8-quinoline-sulfonyl moiety was attached. This new compound is quite water soluble as hydrochloride salt, behaves as a strong CA II inhibitor, and fared better than the parent molecule in lowering IOP in experimental animals. Thus, the tail conferring water solubility to such an enzyme inhibitor is more important for its topical activity as antiglaucoma drug than the heterocyclic/aromatic ring to which the sulfonamido moiety is grafted.

Carbonic anhydrase inhibitors. Water-soluble, topically effective intraocular pressure lowering agents derived from isonicotinic acid and aromatic/heterocyclic sulfonamides: is the tail more important than the ring?

Reaction of twenty aromatic/heterocyclic sulfonamides containing a free amino, imino, hydrazino or hydroxyl group, with isonicotinoyl chloride afforded a series of water-soluble compounds (as hydrochloride or triflate salts). The new derivatives were examined as inhibitors of three carbonic anhydrase (CA) isozymes, CA I, II (cytosolic forms) and IV (membrane-bound form). Efficient inhibition was observed against all three isozymes, but especially against CA II and CA IV (K(I) in the nanomolar range), the two isozymes known to play a critical role in aqueous humor secretion within the ciliary processes of the eye. Some of the most potent inhibitors synthesized were applied as 2% water solutions directly into the eye of normotensive or glaucomatous albino rabbits. Very strong intraocular pressure (IOP) lowering was observed for many of them, and the active drug was detected in eye tissues and fluids. According to others the IOP lowering effect of topically effective antiglaucoma sulfonamides is due to the intrinsic nature of the specific heterocyclic sulfonamide considered, among which the thienothiopyran-2-sulfonamide derivatives represent the best studied case e.g. dorzolamide. In order to prove that the tail (in this case the isonicotinoyl moiety) conferring water solubility to a sulfonamide CA inhibitor is more important than the ring to which the sulfonamido group is grafted a dorzolamide derivative to which the isonicotinoyl moiety was attached was also prepared. This new compound is more water soluble than dorzolamide (as hydrochloride salt), behaves as a strong CA II inhibitor and acts similarly to the parent derivative in lowering IOP in experimental animals. Thus, it seems that the tail conferring water solubility is more important for topical activity as an antiglaucoma drug than the heterocyclic/aromatic ring to which the sulfonamido moiety is attached.

Carbonic anhydrase inhibitors. Schiff bases of some aromatic sulfonamides and their metal complexes: towards more selective inhibitors of carbonic anhydrase isozyme IV

Reaction of three aromatic sulfonamides possessing a primary amino group, i.e., sulfanilamide, homosulfanilamide and p-aminoethyl-benzenesulfonamide with heterocyclic and aromatic aldehydes afforded a series of Schiff bases. Metal complexes of some of these Schiff bases with divalent transition ions such as Zn(II), Cu(II), Co(II) and Ni(II) have also been obtained. The new compounds were assayed as inhibitors of three isozymes of carbonic anhydrase (CA). Several of the new compounds showed a modest selectivity for the membrane-bound (bovine) isozyme CA IV (bCA IV) as compared to the cytosolic human isozymes hCA I and II, in contrast to classical inhibitors which generally possess a 17-33 times lower affinity for bCA IV. This greater selectivity toward bCA IV is due mainly to a slightly decreased potency against hCA II relative to classical inhibitors. However, metal complexes of these Schiff bases possessed an increased affinity for hCA II, being less inhibitory against bCA IV. The first type of compounds reported here (i.e., the Schiff bases of aromatic sulfonamides with heterocyclic aldehydes) might thus lead to the development of low molecular weight isozyme specific CA IV inhibitors. The difference in affinity for the three isozymes of the inhibitors reported by us here is tentatively explained on the basis of recent X-ray crystallographic studies of these isozymes and their adducts with substrates/inhibitors.

Salivary carbonic anhydrase isoenzyme VI

The carbonic anhydrases (CAs) participate in the maintenance of pH homeostasis in various tissues and biological fluids of the human body by catalysing the reversible reaction CO2 + H2O HCO3- + H+ (Davenport & Fisher, 1938; Davenport, 1939; Maren, 1967). Carbonic anhydrase isoenzyme VI (CA VI) is the only secretory isoenzyme of the mammalian CA gene family. It is exclusively expressed in the serous acinar cells of the parotid and submandibular glands, from where it is secreted into the saliva. In this review, we will discuss recent advances in research focused on the physiological role of salivary CA VI in the oral cavity and upper alimentary canal.

Nonstatistical binding of a protein to clustered carbohydrates

Carbohydrate-derivatized self-assembled monolayers (SAMs) are used as a model system to address issues involving cell-surface carbohydrate-protein interactions. Here we examine the influence of carbohydrate surface density on protein-binding avidity. We show that the binding selectivity of Bauhinia purpurea lectin switches from one carbohydrate ligand to another as the surface density of the carbohydrate ligands increases from values of chi(sugar) approximately 0.1-1.0. Polyvalent binding is possible at all surface densities investigated; hence, the switch in selectivity is not due simply to the achievement of a critical density that permits polyvalent contacts. Instead, secondary interactions at high surface densities promote a switch in carbohydrate-binding selectivity. These findings may have implications for how changes in the composition and the density of cell-surface carbohydrates influence biological recognition processes and regulatory pathways.

Kinetic and spectroscopic characterization of the gamma-carbonic anhydrase from the methanoarchaeon Methanosarcina thermophila

The zinc and cobalt forms of the prototypic gamma-carbonic anhydrase from Methanosarcina thermophila were characterized by extended X-ray absorption fine structure (EXAFS) and the kinetics were investigated using steady-state spectrophotometric and (18)O exchange equilibrium assays. EXAFS results indicate that cobalt isomorphously replaces zinc and that the metals coordinate three histidines and two or three water molecules. The efficiency of either Zn-Cam or Co-Cam for CO(2) hydration (k(cat)/K(m)) was severalfold greater than HCO(3-) dehydration at physiological pH values, a result consistent with the proposed physiological function for Cam during growth on acetate. For both Zn- and Co-Cam, the steady-state parameter k(cat) for CO(2) hydration was pH-dependent with a pK(a) of 6.5-6.8, whereas k(cat)/K(m) was dependent on two ionizations with pK(a) values of 6.7-6.9 and 8.2-8.4. The (18)O exchange assay also identified two ionizable groups in the pH profile of k(cat)/K(m) with apparent pK(a) values of 6.0 and 8.1. The steady-state parameter k(cat) (CO(2) hydration) is buffer-dependent in a saturable manner at pH 8. 2, and the kinetic analysis suggested a ping-pong mechanism in which buffer is the second substrate. The calculated rate constant for intermolecular proton transfer is 3 x 10(7) M(-1) s(-1). At saturating buffer concentrations and pH 8.5, k(cat) is 2.6-fold higher in H(2)O than in D(2)O, suggesting that an intramolecular proton transfer step is at least partially rate-determining. At high pH (pH > 8), k(cat)/K(m) is not dependent on buffer and no solvent hydrogen isotope effect was observed, consistent with a zinc hydroxide mechanism. Therefore, at high pH the catalytic mechanism of Cam appears to resemble that of human CAII, despite significant structural differences in the active sites of these two unrelated enzymes.

Biodegradable polymeric microcellular foams by modified thermally induced phase separation method

Thermally induced phase separation (TIPS) for the fabrication of porous foams based on various biodegradable polymers of poly(L-lactic acid) and its copolymers with D-lactic acid and/or glycolic acid is presented. Diverse foam morphologies were obtained by systematically changing several parameters involved in the TIPS process, such as polymer type and concentration, coarsening conditions, solvent/nonsolvent composition, and the presence of an additive. The produced foams had microcellular structures with average pore diameters ranging from 1 to 30 microns depending on the process parameters, which were characterized by scanning electron microscopy (SEM) and mercury intrusion porosimetry. Additionally, Pluronic F127 was used as an additive porogen to control the pore geometry and size.

Human lens carbonic anhydrases. Purification and properties

PURPOSE

To isolate and characterize carbonic anhydrase (CA) isozymes of human lenses.

METHODS

Affinity chromatography was used to separate CA isozymes, as monitored by an immunosorbent assay. Amino acid analysis was done on the antigenic CAII. CA catalytic activity and its sensitivity to inhibition was measured on soluble and membrane-bound CA isozymes.

RESULTS

The lens contains 0.25, 9, and 2 microg/g wet weight of CAI, II, and III, respectively. Almost all of the CA catalytic activity originates from CAII. Plasma membranes had a CA activity that was inhibited like the membrane-bound isozyme CAIV CONCLUSIONS: CA activity in human lenses originates from CAI, II and III in the cytoplasm, and from CAIV at plasma membranes of lens epithelium and fibres. CA probably functions like CA in erythrocytes, by facilitating CO2 transport. CAII and CAIV are probably also involved in translenticular ion transport. Chronic intake of CA inhibitors does not seem to induce cataract formation.

Carbonic anhydrase catalyzes cyanamide hydration to urea: is it mimicking the physiological reaction?

The interaction of human carbonic anhydrase (hCA) isozymes I and II with cyanamide, a linear molecule isoelectronic with the main physiological substrate of the enzyme, CO(2), was investigated through spectroscopic, kinetic, and X-ray crystallographic studies. We show here that cyanamide is hydrated to urea in the presence of CAs, and that it also acts as a weak non-competitive inhibitor (K(I)=61+/-3 mM and 238+/-9 mM for hCA II and hCA I, respectively) towards the esterasic activity of these enzymes, as tested with 4-nitrophenyl acetate. Changes in the spectrum of the Co(II)-hCA II derivative observed in the presence of cyanamide suggest that it likely binds the metal ion within the CA active site, adding to the coordination sphere, not substituting the metal-bound solvent molecule. It thereafter undergoes a nucleophilic attack from the metal-bound hydroxide ion, forming urea which remains bound to the metal, as observed in the X-ray crystal structure of hCA II soaked in cyanamide solutions for several hours. The urea molecule is directly coordinated to the active site Zn(II) ion through a protonated nitrogen atom. Several hydrogen bonds involving active site residues Thr199 and Thr200 as well as three water molecules (Wat99, Wat122, and Wat123) further stabilize the urea-hCA II adduct. Kinetic studies in solution further proved that urea acts as a tight binding inhibitor of the two isozymes hCA I and hCA II, with very slow binding kinetics (k(on) = 2.5 x 10(-5)s(-1)M(-1)). A mechanism to explain the hydration process of cyanamide by CAs, as well as the tight binding of urea in the active site, is also proposed based on the hypothesis that urea is deprotonated when bound to the enzyme. Cyanamide is thus the first true suicide substrate of this enzyme for which binding has been documented by means of X-ray crystallographic and spectroscopic studies.

Secondary ligands enhance affinity at a designed metal-binding site

BACKGROUND

Specific interactions of metal ions with proteins are central to all life processes. The varied functions enabled by this cooperation are a consequence of strict control of the binding-site environment, particularly the number, type and geometry of metal-coordinating sidechains. Attempts to mimic these characteristics in the de novo design of metal-binding sites have thus far concentrated primarily on metal recruitment and not on affecting site function through systematic fine-tuning of the metal environment.

RESULTS

A designed tetrahedral Zn(II)-binding site in a variant of the B1 domain of IgG-binding protein G has been expanded by introducing 'secondary ligands'. These interactions were engineered to stabilize the positions of the metal-coordinating histidine residues while retaining the desired coordination geometry. Each mutation increased the protein's affinity for metal, and combining two secondary ligands demonstrated that these enhancements are additive. These results mimic the effects of altering similar interactions observed in the native Zn(II)-binding site of carbonic anhydrase. In the B1 system, this enhanced affinity for metal is observed despite a substantial decrease in protein secondary structure.

CONCLUSIONS

The intended effects of secondary ligand addition on metal affinity were observed in each mutant and demonstrated to be additive. Addition of metal also stabilized the protein's structure, partially offsetting the destabilizing effect of the mutations. These results represent a successful first attempt at designing an extended metal-binding site environment and illustrate the importance of including secondary interactions in the design of metal-binding sites.

Omeprazole has a dual mechanism of action: it inhibits both H(+)K(+)ATPase and gastric mucosa carbonic anhydrase enzyme in humans (in vitro and in vivo experiments)

In this study our experiments followed in vitro and in vivo the effect of omeprazole on purified and erythrocyte carbonic anhydrase (CA) I and II isozymes, as well as on gastric mucosa CA IV in humans. Our in vitro results show that omeprazole-induced inhibition of purified CA I and CA II and gastric mucosa CA IV is dose- and pH-dependent. In vivo, the i.v. administration of omeprazole in humans in therapeutic doses produced a decrease in erythrocyte CA I and CA II activity, as well as in gastric mucosa CA I, II, and IV. Regarding CA IV, the results lead to the conclusion that omeprazole selectively inhibits gastric mucosa CA IV and does not modify the activity of the same isozyme from the kidney and lung, indicating organ specificity. Our results strongly suggest that omeprazole has a dual mechanism of action: H(+)K(+)ATPase inhibition and gastric mucosa CA inhibition, and that these enzymes may be functionally coupled. This 2-fold mechanism of action could explain the greater effectiveness of substituted benzimidazoles as compared with other therapies.

Comparison of binary and 2D QSAR analyses using inhibitors of human carbonic anhydrase II as a test case

Binary and conventional 2D QSAR have been derived for a set of carbonic anhydrase II (CA II) inhibitors. An overall predictive accuracy of 94% was obtained by binary QSAR and of 84% by 2D QSAR model. For both models, preferred molecular descriptor sets were identified, which were overlapping but not identical. Both binary and 2D QSAR captured important molecular features of CA II inhibitors, notably the presence of a sulfonamido group, which is critical for binding, but also hydrophobicity. Promising results were obtained when the derived QSAR models were used to test a set of CA II inhibitors not included in the training set. In binary QSAR, previously unobserved boundary effects were detected both in the analysis of known inhibitors and when screening a large combinatorial library for putative inhibitors. The complementary use of binary and conventional 2D QSAR is thought to increase the accuracy of the lead discovery process by QSAR techniques.

Human mitochondrial carbonic anhydrase VB. cDNA cloning, mRNA expression, subcellular localization, and mapping to chromosome x

A cDNA clone for a novel carbonic anhydrase (CA) isozyme was isolated from human pancreas and salivary glands. The cDNA sequence of 1182 base pairs encoded a 317-amino acid protein with a predicted mass of 36.4 kDa. The highest similarity of this cDNA and the deduced amino acid sequence is to human CA V (mitochondrial CA), hereafter referred to as CA VA. Recombinant protein expressed in COS-7 cells transfected with this cDNA clone was enriched in a mitochondrial fraction. Confocal fluorescence microscopy showed cytoplasmic granular signals in COS-7 cells expressing a fusion protein of the novel CA and green fluorescent protein. Several lines of evidence suggest that the cDNA clone presented herein encodes a novel human mitochondrial CA isozyme, designated CA VB. CA VB has a hydrophobic N-terminal mitochondrial signal sequence (33 amino acid residues). Western blot analysis showed a 36-kDa protein precursor and a 32-kDa mature protein for CA VB. Similar to CA VA, CA VB is a "low activity" enzyme with a sensitivity to acetazolamide. The CA VB gene is located on Xp22.1. Northern blot analysis in normal human tissues demonstrated expression of a 1.3-kilobase transcript in heart and skeletal muscle, and reverse transcription-polymerase chain reaction analysis showed expression of CA VB in pancreas, kidney, salivary glands, and spinal cord but not in liver. CA VA mRNA expression was observed only in liver. These findings indicate these are two genetically distinct isoforms of human CA V, designated CA VA and CA VB, which have different patterns of tissue-specific distribution, suggest different physiological roles for the two mitochondrial isozymes.

Novel carbonic anhydrase isozymes I, II and IV activators incorporating sulfonyl-histamino moieties

Sulfonylamido(ureido) derivatives of histamine were synthesized by an original procedure in order to obtain tight-binding activators of the zinc enzyme carbonic anhydrase (CA), exploiting the binding energy of the alkyl/arylsulfonyl moieties with amino acid residues at the entrance of the active site. In contrast to the lead molecule, histamine, the new derivatives possessed higher affinity for three different CA isozymes, as evidenced by compairing the affinity constants of these compounds for isozyme CA II.

Metal binding specificity in carbonic anhydrase is influenced by conserved hydrophobic core residues

The role of highly conserved aromatic residues surrounding the zinc binding site of human carbonic anhydrase II (CAII) in determining the metal ion binding specificity of this enzyme has been examined by mutagenesis. Residues F93, F95, and W97 are located along a beta-strand containing two residues that coordinate zinc, H94 and H96, and these aromatic amino acids contribute to the high zinc affinity and slow zinc dissociation rate constant of CAII [Hunt, J. A., and Fierke, C. A. (1997) J. Biol. Chem. 272, 20364-20372]. Substitutions of these aromatic amino acids with smaller side chains enhance the copper affinity (up to 100-fold) while decreasing the affinity of both cobalt and zinc, thereby altering the metal binding specificity up to 10(4)-fold. Furthermore, the free energy of the stability of native CAII, determined by solvent-induced denaturation, correlates positively with increased hydrophobicity of the amino acids at positions 93, 95, and 97 as well as with cobalt and zinc affinity. Conversely, increased copper affinity correlates with decreased protein stability. Zinc specificity is therefore enhanced by formation of the native enzyme structure. These data suggest that the hydrophobic cluster in CAII is important for orienting the histidine residues to stabilize metals bound with a distorted tetrahedral geometry and to destabilize the trigonal bipyramidal geometry of bound copper. Knowledge of the structural factors that lead to high metal ion specificity will aid in the design of metal ion biosensors and de novo catalytic sites.

Renal carbonic anhydrase activity in DBA/2FG-pcy/pcy mice with inherited polycystic kidney disease

DBA/2FG-pcy/pcy (D2-pcy) mice are a hereditary murine model of slowly progressive polycystic kidney disease (PKD) and characterized by the persistent excretion of acidic urine, in association with polyuria, after weaning. In this study, the activity of carbonic anhydrase (CA) and it histological distribution in the kidney of D2-pcy mice were investigated by immunohistochemistry. Significantly higher CA activity was detected in the cytosolic, but not membrane, fraction of kidney homogenates in 5-week-old D2-pcy mice than in age-matched, control DBA/2 (D2) mice, and a more rapid rate of urine acidification was noted in 11-week-old mice when acetazolamide, an inhibitor of the enzyme, was administered orally. By immunohistochemistry for the major renal CA isoenzyme (CA II), epithelial cells in the distal straight tubules and the cortical collecting ducts were stained intensely, whereas those of the proximal convoluted tubules had only weak and diffuse staining. The glomeruli, the proximal straight tubules and the ascending thin limb of Henle's loop were almost free from staining. In the cells lining cysts and/or dilated tubules, CA II activity was well preserved, although the staining intensity was considerably reduced in fully-flattened, lining cells of cysts, but no difference was found between D2-pcy and D2 mice in any segmental localization of renal CA II activity. From these results it seems that D2-pcy mice in the early stages of the cystic disease continue to secrete excess protons through the CA-mediated reaction that is stimulated for regulation of acid-base balance in the distal portion of the nephron and the collecting duct in kidney. It also suggests that monitoring urine pH may be useful in predicting the effects of early interventions on the progression of slowly developing renal cysts.

A new protein folding screen: application to the ligand binding domains of a glutamate and kainate receptor and to lysozyme and carbonic anhydrase

Production of folded and biologically active protein from Escherichia coli derived inclusion bodies can only be accomplished if a scheme exists for in vitro naturation. Motivated by the need for a rapid and statistically meaningful method of determining and evaluating protein folding conditions, we have designed a new fractional factorial protein folding screen. The screen includes 12 factors shown by previous experiments to enhance protein folding and it incorporates the 12 factors into 16 different folding conditions. By examining a 1/256th fraction of the full factorial, multiple folding conditions were determined for the ligand binding domains from glutamate and kainate receptors, and for lysozyme and carbonic anhydrase B. The impact of each factor on the formation of biologically active material was estimated by calculating factor main effects. Factors and corresponding levels such as pH (8.5) and L-arginine (0.5 M) consistently had a positive effect on protein folding, whereas detergent (0.3 mM lauryl maltoside) and nonpolar additive (0.4 M sucrose) were detrimental to the folding of these four proteins. One of the 16 conditions yielded the most folded material for three out of the four proteins. Our results suggest that this protein folding screen will be generally useful in determining whether other proteins will fold in vitro and, if so, what factors are important. Furthermore, fractional factorial folding screens are well suited to the evaluation of previously untested factors on protein folding.