Rotavirus VP6 protein as a bio-electrochemical scaffold: Molecular dynamics and experimental electrochemistry.

This paper reports a theoretical and experimental investigation on the recombinant protein rotavirus VP6 as a bioelectrochemical interface. Our motivation arises from the highly active zones of VP6 which can interact with biological structures and metals, as well as its useful features such as self-assembly, polymorphism, and active surface charge. A molecular simulation study was performed to analyze the charge transfer properties of theVP6 trimer under an applied electric field. The electrostatic properties were evaluated via the nonlinear second-order Poisson-Boltzmann equation, using finite element methods based on parameter discretization and calculation of solute/solvent interaction forces, which account for mean-field screening effects. The electrochemical study validated the theoretical predictions for VP6 in their different assemblies (trimers and nanotubes) when they are used as electrodes in 10 mM K3[Fe(CN)6], 1 M KCl. Applying a potential sweep promotes charge transfer, facilitates redox activity of the ferricyanide ion. Furthermore, protein assemblies decreased electrode electrical resistance and enabled gold particle electrodeposition on the protein VP6. These results suggest that VP6 is a promising conductive biomaterial that promotes charge transfer of redox probes and could be used as a new scaffold to create bio-electrochemical interfaces.

Delivery of glutamine synthetase gene by baculovirus vectors: a proof of concept for the treatment of acute hyperammonemia.

Hyperammonemia, a condition present in patients with urea cycle disorders (UCDs) or liver diseases, can cause neuropsychiatric complications, which in the worst cases result in brain damage, coma or death. Diverse treatments exist for the treatment of hyperammonemia, but they have limited efficacy, adverse effects and elevated cost. Gene therapy is a promising alternative that is explored here. A baculovirus, termed Bac-GS, containing the glutamine synthetase (GS) gene was constructed for the in vitro and in vivo treatment of hyperammonemia. Transduction of MA104 epithelial or L6 myoblast/myotubes cells with Bac-GS resulted in a high expression of the GS gene, an increase in GS concentration, and a reduction of almost half of exogenously added ammonia. When Bac-GS was tested in an acute hyperammonemia rat model by intramuscularly injecting the rear legs, the concentration of ammonia in blood decreased 351 µM, in comparison with controls. A high GS concentration was detected in gastrocnemius muscles from the rats transduced with Bac-GS. These results show that gene delivery for overexpressing GS in muscle tissue is a promising alternative for the treatment of hyperammonemia in patients with acute or chronic liver diseases and hepatic encephalopathy or UCD.

Crystallization and identification of the glycosylated moieties of two isoforms of the main allergen Hev b 2 and preliminary X-ray analysis of two polymorphs of isoform II.

Latex from Hevea brasiliensis contains several allergenic proteins that are involved in type I allergy. One of them is Hev b 2, which is a beta-1,3-glucanase enzyme that exists in different isoforms with variable glycosylation content. Two glucanase isoforms were isolated from trees of the GV-42 clone by gel filtration, affinity and ion-exchange chromatography. Isoform I had a carbohydrate content of about 20%, with N-linked N-acetyl-glucosamine, N-acetyl-galactosamine, fucose and galactose residues as the main sugars, while isoform II showed 6% carbohydrate content consisting of N-acetyl-glucosamine, fucose, mannose and xylose. Both isoforms were crystallized by the hanging-drop vapour-diffusion method. Isoform I crystals were grown using 0.2 M trisodium citrate dihydrate, 0.1 M Na HEPES pH 7.5 and 20%(v/v) 2-propanol, but these crystals were not appropriate for data collection. Isoform II crystals were obtained under two conditions and X-ray diffraction data were collected from both. In the first condition (0.2 M trisodium citrate, 0.1 M sodium cacodylate pH 6.5, 30% 2-propanol), crystals belonging to the tetragonal space group P4(1) with unit-cell parameters a = b = 150.17, c = 77.41 A were obtained. In the second condition [0.2 M ammonium acetate, 0.1 M trisodium citrate dihydrate pH 5.6, 30%(w/v) polyethylene glycol 4000] the isoform II crystals belonged to the monoclinic space group P2(1), with unit-cell parameters a = 85.08, b = 89.67, c = 101.80 A, beta = 113.6 degrees. Preliminary analysis suggests that there are four molecules of isoform II in both asymmetric units.

Comparison of growth and recombinant protein expression in two different insect cell lines in attached and suspension culture.

Culture conditions required for obtaining maximum recombinant protein concentrations from two cell lines, Spodoptera frugiperda (IPLBeta-Sf21-AE) and Trichoplusia ni (Tn 5Beta-1-4), were determined in this work. Conditions studied include mode of culture (suspended vs attached), agitation rates, inoculum sizes, cell concentration at the time of infection, and various serum-free media (SFM). Results were compared with the performance of attached cultures in TnM-FH with 10% fetal bovine serum. Growth rates in the different culture media tested were similar, but the cell numbers achieved (i.e., yield) improved 2 to 2.7-fold in SFM over cultures in TnM-FH. Agitation rates of 150-160 rpm were necessary for maximum growth of suspended Tn 5Beta-1-4 cells compared to 125-150 rpm for Sf-21 cells. An inoculum size of 5 x 10(5) cells/mL gave good growth rates and optimum biomass yields for both cell lines. Cultures of both cell lines were infected with viruses encoding for beta-galactosidase or human secreted alkaline phosphatase (seAP). Protein expression in TnM-FH in attached culture showed that Tn 5Beta-1-4 cells are 2-4.5 times more productive on a per cell basis than Sf-21 cells grown under similar conditions. Production of beta-galactosidase in Sf-21 cells increased 50% in suspension cultures with SFM compared to attached cultures in TnM-FH, but seAP expression was essentially unchanged by culture techniques. The Tn 5Beta-1-4 cells produced 2.6-4.4 and 2.7-3 times more beta-galactosidase and seAP, respectively, in SFM in suspension compared to Sf-21 cells. EX-CELL 401 and Sf900-II were formulated as optimized SFM for Sf cell lines. However, in Sf-21 cultures EX-CELL 400 performed better than the other two media, as it increased the beta-galactosidase yield up to 25%. Surprisingly, EX-CELL 401 was the best medium for the production of beta-galactosidase by Tn 5Beta-1-4 cells, resulting in 25% and 69% higher volumetric and specific yields, respectively, compared to EX-CELL 405 which was formulated for this specific cell line. These results show that even when culture media are designed for maximal growth of a specific cell line, other media may provide the best conditions for protein production.

Parameters that determine virus adsorption kinetics: toward the design of better infection strategies for the insect cell - baculovirus expression system.

High productivities of bioprocesses involving viruses can be attained through infection strategies based on adequate understanding of parameters ruling cell-virus interactions. Two factors that affect virus binding and infection efficiency were studied: the utilization of an adsorption step, where infection volume at constant cell/virus ratio was varied; and the concentration of fetal bovine serum (FBS). The insect cell-baculovirus expression system and recombinant protein VP4 of rotavirus were used as models. Virus binding kinetics were adequately described by a sigmoidal response curve. The adsorption step, with or without FBS, increased virus attachment rate, whereas it increased bound virus at equilibrium only in FBS-free infections. A first-order dependance of virus attachment on cell concentration was found above 5 x 10(6) cell/mL in infections with 10% FBS. Addition of 10% FBS decreased maximum bound baculovirus and binding rate by as much as 3 times and VP4 concentration up to 4 times. In contrast, heat inactivation of FBS increased bound virus from 20% to over 90%, an increase of 1.4 times compared to FBS-free infections. A direct linear relation was found between attached virus and maximum VP4 concentration for the different FBS concentrations tested, indicating that baculovirus-cell attachment was the limiting step for recombinant protein production. Interestingly, virus progeny accumulation was not affected by differences in virus binding. In conclusion, infection strategies aimed at increasing productivity should be performed at high cell concentrations and without FBS, or with heat-inactivated FBS.

The effect of dissolved oxygen tension and the utility of oxygen uptake rate in insect cell culture.

Dissolved oxygen tension and oxygen uptake rate are critical parameters in animal cell culture. However, only scarce information of such variables is available for insect cell culture. In this work, the effect of dissolved oxygen tension (DOT) and the utility of on-line oxygen uptake rate (OUR) measurements in monitoring Spodoptera frugiperda (Sf9) cultures were determined. Sf9 cells were grown at constant dissolved oxygen tensions in the range of 0 to 30%. Sf9 metabolism was affected only at DOT below 10%, as no significant differences on specific growth rate, cell concentration, amino acid consumption/production nor carbohydrates consumption rates were found at DOT between 10 and 30%. The specific growth rate and specific oxygen uptake rate followed typical Monod kinetics with respect to DOT. The calculated µ(max) and [Formula: see text] max were 0.033 h(-1) and 3.82×10(-10) mole cell(-1)h(-1), respectively, and the corresponding saturation constants were 1.91 and 1.57%, respectively. In all aerated cultures, lactate was consumed only after glucose and fructose had been exhausted. The yield of lactate increased with decreasing DOT. It is proposed, that an 'apparent' DOT in non-instrumented cultures can be inferred from the lactate yield of bioreactors as a function of DOT. Such a concept, can be a useful and important tool for determining the average dissolved oxygen tension in non-instrumented cultures. It was shown that the dynamic behavior of OUR can be correlated with monosaccharide (fructose and glucose) depletion and viable cell concentration. Accordingly, OUR can have two important applications in insect cell culture: for on-line estimation of viable cells, and as a possible feed-back control variable in automatic strategies of nutrient addition.