Molecular recognition and binding between human plasminogen Kringle 5 and α-chain of human complement component C3b by frontal chromatography and dynamics simulation

The binding and molecular recognition between α-chain of human complement C3b (α-chain of C3b) and human plasminogen Kringle 5 (Kringle 5) were studied and explored by frontal chromatography and dynamics simulation in the combination of bio-specific technologies. The specific interaction between the α-chain of C3b and Kringle 5 was initially confirmed by ligand blot and ELISA (Kd = 4.243×10-6 L/mol). Furthermore, the binding determination conducted via frontal chromatography showed that the presence of a single binding site between them, with the binding constant of 2.98 × 105 L/mol. Then the molecular recognition by dynamics simulation and molecular docking showed that there were 9 and 13 amino acid residues respective in the Kringle 5 and α-chain of C3b directly implicated in the binding and the main stabilizing forces were electrostatic force (-55.99 ± 11.82 kcal/mol) and Van der Waals forces (-42.70 ± 3.45 kcal/mol). Additionally, a loop structure (65-71) in Kringle 5 underwent a conformational change from a random structure to an α-helix and a loop structure (417-425) in α-chain of C3b was closer to the molecular center, both of them were more conducive to the binding between them. Meanwhile, the involvement of the lysine binding site of Kringle 5 played an important role in the binding process. In addition, the erythrocyte-antibody complement rosette assay substantiated that the presence of Kringle 5 hindered the transportation of α-chain of C3b to antigen-antibody complex in a dose-dependent manner. These findings collectively indicated that the α-chain of C3b is very likely a receptor protein for Kringle 5, which provides a methodology for other similar investigations and valuable insights into expansion of the pharmacological effects and potential application of Kringle 5 in immune-related diseases.

Radiostrontium determination by combination of automated Sr isolation and "on-column" Cherenkov detection using chromatographic model

A novel analytical solution of non-linear chromatography in case of parabolic isotherm for frontal analysis was obtained by combination of Cole-Hopf and Laplace transform. It was used for simulation of strontium capturing on chromatographic column with aim to improve quantitative determination of low-level 90Sr activities. From the experimentally determined breakthrough curves, the retention factor and the number of theoretical plates were calculated using the Glueckauf and Wenzel relations and by fitting the breakthrough curves for the linear isotherm using MatLab. These were used to simulate the breakthrough curves using a parabolic isotherm solution where the non-linear term of the isotherm was taken as a small negative deviation of the retention factor. On the base of theoretical prediction and experimental data, procedure for automated capturing of strontium on chromatographic column with specific dimension and off line "on-column" Cherenkov detection on commercial ultra low-level liquid scintillation counter was developed. It was shown that analytical solution for parabolic isotherm in comparison with solution for linear isotherm gives better prediction of mass of captured Sr on column filled with small amount of Sr resin and SuperLig®620 in case of elevated Sr concentration, even when non-linear effect is not obvious. The solution also makes it possible to predict the mass of resin required for strontium isolation at 100% yield under given conditions. Considering the limited dimensions of the column, and consequently small mass of the resin in them, it resulted in the low efficiency of the columns, which, however, did not affect the yield in real conditions of isolation. The results have shown that the yields achieved after isolation on SuperLig®620 from real samples are 100%. In addition, it is shown that captured 90Sr can be detected through 90Y ingrowth, on column filled with strontium specific resin, with Cherenkov detection efficiency of at least 50%. The efficiency may be enhanced to 60%, depending on parameters which can affect detection efficiency change (type of column, resin type, surrounding solution, etc.). The developed procedures enable quantitative determination of 90Sr in natural water samples with MDAC below 12 mBq l-1 and solid (soil and vegetation) samples with MDAC below 6 Bq kg-1 within 2-3 days. The proposed solution may easily be implemented in radiochemical laboratories where this type of analysis is routinely done within environmental monitoring or other purposes.

Resin structure impacts two-component protein adsorption and separation in anion exchange chromatography

The influence of the resin structure, on the competitive binding and separation of a two-component protein mixture with anion exchange resins is evaluated using conalbumin and green fluorescent protein as a model system. Two macroporous resins, one with large open pores and one with smaller pores, are compared to a resin with grafted polymers. Investigations include measurements of single and two-component isotherms, batch uptake kinetics and two-component column breakthrough. On both macroporous resins, the weaker binding protein, conalbumin, is displaced by the stronger binding green fluorescent protein. For the large pore resin, this results in a pronounced overshoot and efficient separation by frontal chromatography. The polymer-grafted resin exhibits superior capacity and kinetics for one-component adsorption, but is unable to achieve separation due to strongly hindered counter-diffusion. Intermediate separation efficiency is obtained with the smaller pore resin. Confocal laser scanning microscopy provides a mechanistic explanation of the underlying intra-particle diffusional phenomena revealing whether unhindered counter-diffusion of the displaced protein can occur or not. This study demonstrates that the resin's intra-particle structure and its effects on diffusional transport are crucial for an efficient separation process. The novelty of this work lies in its comprehensive nature which includes examples of the three most commonly used resin structures: a small pore agarose matrix, a large-pore polymeric matrix, and a polymer grafted resin. Comparison of the protein adsorption properties of these materials provides valuable clues about advantages and disadvantages of each for anion exchange chromatography applications.

Sample displacement chromatography of monoclonal antibody charge variants and aggregates

The rise of biosimilar monoclonal antibodies has renewed the interest in monoclonal antibody (mAb) charge variants composition and separation. The sample displacement chromatography (SDC) has the potential to overcome the low separation efficiency and productivity associated with bind-elute separation of mAb charge variants. SDC in combination with weak cation exchanging macroporous monolithic chromatographic column was successfully implemented for a separation of charge variants and aggregates of monoclonal IgG under overloading conditions. The charge variants composition was at-line monitored by a newly developed, simple and fast analytical method, based on weak cation exchange chromatography. It was proven that basic charge variants acted as displacers of IgG molecules with lower pI, when the loading was performed 1 to 1.5 pH unit below the pI of acidic charge variants. The efficiency of the SDC process is flow rate independent due to a convection-based mass transfer on the macroporous monolith. The productivity of the process at optimal conditions is 35 mg of purified IgG fraction per milliliters of monolithic support with 75-80% recovery. As such, an SDC approach surpasses the standard bind-elute separation in the productivity for a factor of 3, when performed on the same column. The applicability of the SDC approach was confirmed for porous particle-based column as well, but with 1.5 lower productivity compared to the monoliths.

Design space and robustness analysis of batch and counter-current frontal chromatography processes for the removal of antibody aggregates

Increasing molecular diversity and market competition requires biopharmaceutical manufacturers to intensify their processes. In this respect, frontal chromatography on cation exchange resins has shown its potential to effectively remove aggregates. However, yield losses during the wash step need to be accepted in order to ensure robust product quality. In this work, we present a novel counter-current frontal chromatography process called Flow2, which uses inline dilution during an interconnected wash phase to allow high monomer recovery without contaminating the product pool with impurities. Its model-based design spaces under purity and yield constraints are compared with those corresponding to traditional batch processes in terms of size and process attributes yield and productivity. The Flow2 process shows the largest extent of feasible operating points independent of feed conditions. Thereby, it allows the implementation of higher ionic strength wash, thus widening the range of operating conditions resulting in yields above 95% compared to batch processes. Productivities of batch and counter-current processes are the same at short regeneration times and equal residence time. However, long regeneration times, while influencing the size of the Flow2 design space, are not detrimental for its productivity resulting in twice as high values as obtained for the batch process. Furthermore, process robustness is evaluated by the ability of the process to maintain the required product quality when subjected to process parameter perturbations. It is found that the Flow2 process is able to retain a larger design space associated also with higher yields showing its ability to improve process attributes without sacrificing robustness at the same time.

Breakthrough during air sampling with polyurethane foam: What do PUF 2/PUF 1 ratios mean?

Frontal chromatography theory is applied to describe movement of gaseous semivolatile organic compounds (SVOCs) through a column of polyurethane foam (PUF). Collected mass fractions (F_C) are predicted for sample volume/breakthrough volume ratios (τ = V_S/V_B) up to 6.0 and PUF bed theoretical plate numbers (N) from 2 to 16. The predictions assume constant air concentrations and temperatures. Extension of the calculations is done to relate the collection efficiency of a 2-PUF train (F_C1+2) to the PUF 2/PUF 1 ratio. F_C1+2 exceeds 0.9 for PUF 2/PUF 1 ≤ 0.5 and lengths of PUF commonly used in air samplers. As the PUF 2/PUF 1 ratio approaches unity, confidence in these predictions is limited by the analytical ability to distinguish residues on the two PUFs. Field data should not be arbitrarily discarded because some analytes broke through to the backup PUF trap. The fractional collection efficiencies can be used to estimate air concentrations from quantities retained on the PUF trap when sampling is not quantitative.

Characterization of a multiple endogenously expressed adenosine triphosphate-binding cassette transporters using nuclear and cellular membrane affinity chromatography columns

Glioblastoma multiforme is an aggressive form of human astrocytoma, with poor prognosis due to multi-drug resistance to a number of anticancer drugs. The observed multi-drug resistance is primarily due to the efflux activity of ATP-Binding Cassette (ABC) efflux transporters such as Pgp, MRP1 and BCRP. The expression of these transporters has been demonstrated in nuclear and cellular membranes of the LN-229 human glioblastoma cell line. Nuclear membrane and cellular membrane fragments from LN-229 cells were immobilized on the IAM stationary phase to create nuclear and cellular membrane affinity chromatography columns, (NMAC(LN-229)) and (CMAC(LN-229)), respectively. Pgp, MRP1 and BCRP transporters co-immobilized on both columns were characterized and compared by establishing the binding affinities for estrone-3-sulfate (3.8 vs. 3.7μM), verapamil (0.6 vs. 0.7μM) and prazosin (0.099 vs. 0.033μM) on each column and no significant differences were observed. Since the marker ligands had overlapping selectivities, the selective characterization of each transporter was carried out by saturation of the binding sites of the non-targeted transporters. The addition of verapamil (Pgp and MRP1 substrate) to the mobile phase allowed the comparative screening of eight compounds at the nuclear and cellular BCRP using etoposide as the marker ligand. AZT increased the retention of etoposide (+15%), a positive allosteric interaction, on the CMAC(LN-229) column and decreased it (-5%) on the NMAC(LN-229), while the opposite effect was produced by rhodamine. The results indicate that there are differences between the cellular and nuclear membrane expressed BCRP and that NMAC and CMAC columns can be used to probe these differences.