Mechanisms leading to an oriented immobilization of recombinant proteins derived from the P24 capsid of HIV-1 onto copolymers

Additional stabilization of stem bromelain coupled to a thermosensitive polymer by uniform orientation and using polyclonal antibodies

Stem bromelain was covalently coupled to a thermosensitive polymer of N-isopropylacrylamide (p(NIPAm)) either through the amino groups of the enzyme (randomly coupled) or via the lone oligosaccharide chain (uniformly coupled). The enzyme coupled via the oligosaccharide chain exhibited better access to the substrate casein as compared to the preparation in which the amino groups formed the point of contact between the enzyme and the polymer. Native bromelain exhibited a pH optimum of 8.0 and a broad pH-activity profile. The polymer-coupled preparations exhibited broader pH-activity profiles and shifting of pH optimum to 10.0 at 35 degrees C. At 25 degrees C, the shifting of pH optimum was observed for the randomly coupled enzyme only. The temperature-activity profiles of bromelain coupled to p(NIPAm) also showed appreciable broadening and the preparations retained greater fraction of maximum activity above the temperature optimum. The optimum temperature of the uniformly oriented preparation also rose to 70 degrees C. Inactivation rates of the polymer-coupled bromelain were remarkably low at 60 degrees C as compared to the native protease, and binding of antibromelain antibodies improved the resistance to inactivation of the polymer-coupled preparations. The cleavage patterns of hemoglobin and IgG by the native bromelain and the polymer-coupled preparations were comparable.

Electroaddressed immobilization of recombinant HIV-1 P24 capsid protein onto screen-printed arrays for serological testing

A serological chemiluminescent biochip was designed based on screen-printed electrode arrays composed of nine 1-mm(2) electrodes. Arrays were shown to be produced with good batch-to-batch reproducibility (standard deviations of 4.4 and 12.0% for ferricyanide oxidation potential and current, respectively) and very good reproducibility within a particular array (2.0 and 7.5% standard deviations for the same controls). Electrode arrays were used to electroaddress various bioconjugate structures comprising a recombinant HIV-1 P24 capsid protein (RH24K) in polypyrrole film. Entrapment of RH24K preimmobilized onto maleic anhydride-alt-methyl vinyl ether copolymer was shown to be the more efficient immobilization procedure. This addressed sensing layer enabled the detection of anti-P24 antibodies at a concentration of 3.5 ng/ml through peroxidase-labeled anti-human immunoglobulin G reaction. The biochip was used to perform an HIV-1 serological test in human sera. HIV-1 seropositive and seronegative sera were easily discriminated using serum dilutions greater than 1/10,000.

Latex bead immobilisation in PDMS matrix for the detection of p53 gene point mutation and anti-HIV-1 capsid protein antibodies

Two diagnostic chemiluminescent biochips were developed for either the detection of p53 gene point mutation or the serological detection of anti-HIV-1 p24 capsid protein. Both biochips were composed of 24 microarrays of latex beads spots (4x4) (150 microm in diameter, 800 microm spacing) entrapped in a poly(dimethylsiloxane) elastomer (PDMS). The latex beads, bearing oligonucleotide sequences or capsid protein, were spotted with a conventional piezoelectric spotter and subsequently transferred at the PDMS interface. The electron microscopy observation of the biochips showed how homogeneous and well distributed the spots could be. Point mutation detection on the codon 273 of the p53 gene was performed on the basis of the melting temperature difference between the perfect match sequence and the one base pair mismatch sequence. The hybridisation of a 20-mer oligonucleotide form the codon 273 including a one base pair mutation in its sequence on a biochip arrayed with non-muted and the muted complementary sequences, enabled a clear discrimination at 56 degrees C between muted and wild sequences. Moreover, the quantitative measurement of the amount of muted sequence in a sample was possible in the range 0.4-4 pmol. Serological measurement of anti-HIV-1 p24 capsid protein on the biochip, prepared with 1-microm-diameter latex beads, enabled the detection of monoclonal antibodies in the range 1.55-775 ng mL(-1). Such a range could be lowered to 0.775 ng mL(-1) when using 50-nm-diameter beads, which generated a higher specific surface. The validation of the biochip for the detection of anti-HIV-1 capsid protein antibodies was performed in human sera from seropositive and seronegative patients. The positivity of the sera was easily discriminated at serum dilutions below 1:1,000.

Antigenicity of Recombinant Proteins after Regioselective Immobilization onto Polyanhydride-Based Copolymers

We previously demonstrated that the introduction of a tag consisting of several contiguous lysines at the N- or C-terminus of a recombinant protein greatly improved the covalent grafting of the protein onto negatively charged maleic anhydride-alt-methyl vinyl ether (MAMVE) copolymer, under many different experimental conditions (Ladavière, C., et al. (1998) Bioconjugate Chem. 9, 655; Allard, L., et al. (2002) Biotechnol. Bioeng. 80, 341). The grafting efficiency was dependent on the charge and amine density of the tag, characteristics which were determined by the tag composition. The six lysine tag (Lys6) was found to be the most efficient (Allard, L., et al. (2001) Bioconjugate Chem. 12, 972). In the present work, the biological activity of Lys6-proteins covalently bound to polymer was investigated. N- or C-terminal Lys6-tagged HIV-1 p24 recombinant proteins (RK24H and RH24K) were grafted onto MAMVE, and the antigenicity each of the bioconjugates was evaluated using six monoclonal antibodies that recognized different epitopes distributed along the protein. We demonstrate that the position of the tag and the hydrolysis rate of the anhydride moieties of the polymer are the two main parameters involved in the conservation of the biological activity of the immobilized protein. We thus present a process which allows an efficient oriented immobilization of proteins onto copolymers with optimal biological activity that is suitable for the controlled production of active bioconjugates.

Versatile method for production and controlled polymer-immobilization of biologically active recombinant proteins

The immobilization of a protein by covalent attachment to a support matrix should involve only functional groups of the protein that are not essential for its biological activity. A general strategy for obtaining recombinant proteins designed for oriented covalent grafting onto copolymers was investigated. The rationale involves the definition of seven p24-derived recombinant proteins as fused to either distant or adjacent tags comprising primary amine rich tag consisting of six contiguous lysines suitable for oriented covalent immobilization and a hexa-histidine tag suitable for metal chelate affinity purification. High-level expression, efficient affinity purification, and coupling yields onto maleic anhydride-alt-methyl vinyl ether copolymers higher than 95% were obtained for all proteins. Afterwards, an investigation of the biological features of the immobilized vs. nonimmobilized protein onto the copolymer allowed us to select one bioconjugate which was used in a diagnostic context, i.e., as a capture antigen in an ELISA format test. Sera from 107 HIV-seropositive individuals at various stages of HIV infection, including two seroconversion panels and 104 healthy HIV-seronegative controls, were tested using either RH24 or RK24H-copolymer coated onto the microtiter plate. These assays showed that the use of such a protein-copolymer bioconjugate allowed detection of lower antibody titers than the RH24 protein, illustrating the potential of applications of such doubly tagged proteins. Thus, a set of expression vectors was designed containing four different combinations of hexa-lysine and hexa-histidine tags and a multiple cloning site, allowing the production of different recombinant fusion proteins suitable for biological reactivity conservation after immobilization.