Biomedical subjects

Valeria Grazú

Publications and source records attributed to Valeria Grazú.

5 recordsLinked to original sources

PubMed2006

Genetic modification of the penicillin G acylase surface to improve its reversible immobilization on ionic exchangers.

A new mutant of the industrial enzyme penicillin G acylase (PGA) from Escherichia coli has been designed to improve its reversible immobilization on anionic exchangers (DEAE- or polyethyleneimine [PEI]-coated agarose) by assembling eight new glutamic residues distributed homogeneously through the enzyme surface via site-directed mutagenesis. The mutant PGA is produced and processed in vivo as is the native enzyme. Moreover, it has a similar specific activity to and shows the same pH activity profile as native PGA; however, its isoelectric point decreased from 6.4 to 4.3. Although the new enzyme is adsorbed on both supports, the adsorption was even stronger when supports were coated with PEI, allowing us to improve the enzyme stability in organic cosolvents. The use of restrictive conditions during the enzyme adsorption on anionic exchangers (pH 5 and high ionic strength) permitted us to still further increase the strength of adsorption and the enzyme stability in the presence of organic solvents, suggesting that these conditions allow the penetration of the enzyme inside the polymeric beds, thus becoming fully covered with the polymer. After the enzyme inactivation, it can be desorbed to reuse the support. The possibility to improve the immobilization properties on an enzyme by site-directed mutagenesis of its surface opens a promising new scenario for enzyme engineering.

Biotechnology↗

PubMed2005

Stabilization of enzymes by multipoint immobilization of thiolated proteins on new epoxy-thiol supports.

The controlled and partial modification of epoxy groups of Eupergit C and EP-Sepabeads with sodium sulfide has permitted the preparation of thiol-epoxy supports. Their use allowed not only the specific immobilization of enzymes through their thiol groups via thiol-disulfide interchange, but also enzyme stabilization via multipoint covalent attachment. Penicillin G acylase (PGA) from Escherichia coli and lipase from Rhizomucor miehei were used as model enzymes. Both enzymes lacked exposed cysteine residues, but were introduced via chemical modification under very mild conditions. In the first moments of the immobilization, a certain percentage of immobilized protein could be released from the support by incubation with DTT; this confirms that the first step was via a thiol-disulfide interchange. Moreover, the promotion of some further epoxy-enzyme bonds was confirmed because no enzyme release was detected after some immobilization time by incubation with DTT. In the case of the heterodimeric PGA, it was possible to demonstrate the formation of at least one epoxy bond per enzyme subunit by analyzing with SDS-PAGE the supernatants obtained after boiling the enzyme derivatives in the presence of mercaptoethanol and SDS. Thermal inactivation studies showed that these multipoint enzyme-support attachments promoted an increase in the stability of the immobilized enzymes. In both cases, the stabilization factor was around 12-15-fold comparing optimal derivatives with their just-thiol immobilized counterparts.

Binding Sites↗

PubMed2004

Stabilization of penicillin G acylase from Escherichia coli: site-directed mutagenesis of the protein surface to increase multipoint covalent attachment.

Three mutations on the penicillin acylase surface (increasing the number of Lys in a defined area) were performed. They did not alter the enzyme's stability and kinetic properties; however, after immobilization on glyoxyl-agarose, the mutant enzyme showed improved stability under all tested conditions (e.g., pH 2.5 at 4 degrees C, pH 5 at 60 degrees C, pH 7 at 55 degrees C, or 60% dimethylformamide), with stabilization factors ranging from 4 to 11 compared with the native enzyme immobilized on glyoxyl-agarose.

Enzyme Stability↗

PubMed2003

Solid-phase reducing agents as alternative for reducing disulfide bonds in proteins.

Disulfide reduction of Kluyveromyces lactis and Aspergillus oryzae beta-galactosidases and beta-lactoglobulin was assessed. Reduction was performed using one of two thiol-containing agents: dithiothreitol (DTT) or thiopropyl-agarose with a high degree of substitution (1000 micromol of SH groups/g of dried gel). Both reductants allowed an increase of three- (for K. lactis beta-galactosidase) and fourfold (for A. oryzae beta-galactosidase) in the initial content of SH groups in the lactases. Nearly sevenfold fewer micromoles of SH groups per milligram of protein were needed to perform the reduction of K. lactis beta-galactosidase with thiopropyl-agarose than for the same reduction with DTT. However, for A. oryzae beta-galactosidase, nearly twice as many micromoles of SH groups per milligram of protein were needed with thiopropylagarose than with DTT. Disulfide bonds in beta-lactoglobulin were not accessible to thiopropyl-agarose, since this reduction was only possible in the presence of 6 M urea. These results proved that highly substituted thiopropyl-agarose is as good a reducing agent as DTT, for the reduction of disulfide bonds in proteins. Moreover, excess reducing agent was very simply separated from the reduced protein by filtration, making it easier to control the reaction and providing reduced protein solutions free of reductant. All these advantages substantially cut down the time required and therefore the cost of the overall process.

Aspergillus oryzae↗

PubMedDate not supplied

Novel bifunctional epoxy/thiol-reactive support to immobilize thiol containing proteins by the epoxy chemistry.

In this manuscript, we present a new bifunctional support containing epoxide and thiol-reactive groups for its use in protein immobilization. In a first step, the proteins are reversibly immobilized by reaction of its thiol groups with the thiol-reactive groups of the support under mild experimental conditions (pH 7.0, 24 degrees C). Then, the remaining epoxides of the support can form irreversible bonds with nucleophile surface groups of the already immobilized protein in a rapid way. The partial derivatization of EP-Sepabeads (a commercial matrix containing 120 micromol epoxy groups/g drained support) was optimized, using dithiotreitol (DTT) as thiolating agent. It was possible to achieve a partial thiolation of the support proportional to the concentration of DTT used (3, 8, and 15 micromol SH groups/g wet support). The remaining epoxide content after the thiolation treatment was high (e.g., nearly 70% for the highest thiolation degree). High immobilization yields were obtained for the three model enzymes selected (60% for Penicillin G acylase, 65% and 100% for K. lactis and E. coli beta-galactosidase, respectively). In all cases, no significant immobilization onto an unmodified epoxy support was found, thus demonstrating that the first step of attachment takes place through thiol-disulfide exchange reactions. In the case of the bifunctional support, progressive formation of enzyme-support attachments involving the epoxy groups was showed by the irreversible covalent attachment of the proteins on the support. The promotion of this multipoint covalent immobilization required long incubation periods at basic pH values.

Dithiothreitol↗