Mechanism of binding of mouse interferon to controlled pore glass

Immunogenicity of recombinant human interferon beta interacting with particles of glass, metal, and polystyrene

Aggregates play a major role in the immunogenicity of recombinant human interferon beta (rhIFNβ), a protein used to treat multiple sclerosis. A possible cause of aggregation is interaction between therapeutic protein and surfaces encountered during processing, storage, and administration. Moreover, proteins may adsorb to particles shed from these surfaces. In this work, we studied the immunogenicity of recombinant human interferon beta-1a (rhIFNβ-1a) interacting with glass microparticles, stainless steel microparticles, and polystyrene nanoparticles. At physiological pH, rhIFNβ-1a readily adsorbed to the particles, while the degree of adsorption was influenced by the ionic strength of the phosphate buffer. Front-face fluorescence showed that the tertiary structure of rhIFNβ-1a slightly changed upon adsorption to glass. The interaction with stainless steel microparticles resulted in increased levels of aggregates in the free protein fraction. Furthermore, protein adsorbed to stainless steel microparticles was more difficult to desorb than protein adsorbed to glass. Incubation with stainless steel considerably enhanced the immunogenicity of rhIFNβ-1a in transgenic mice immune tolerant for human interferon beta. The protein fraction adsorbed on stainless steel particles was responsible for this. In conclusion, rhIFNβ-1a adsorbs to common hydrophilic surface materials, possibly increasing the immunogenicity of the protein.

Preparative protein purification on underivatized silica

This article describes the use of underivatized silica gel as a preparative stationary phase for process purification of proteins. Although silica has been frequently used as a stationary phase backbone matrix, direct adsorption of proteins on underivatized silica has not been widely exploited for industrial applications. In this study an effort was made to fundamentally understand the interaction mechanisms between a protein and silica surface by using several proteins with a wide range of isoelectric points (pIs) and surface hydrophobicity. Interactions in silica were found to be largely dominated by a combination of ionic and hydrophobic forces. Accordingly, a predictive model was derived for describing linear retention of proteins on silica. Finally, a case study is described investigating the role of silica in an industrial purification process. It was found that the integration of the two modes of interaction confers silica with a unique selectivity that can be very effectively utilized in downstream bioprocessing.

Cyclodextrin biospecific-like displacement in dye-affinity chromatography

Interactions between Cibacron Blue F3GA (CB F3GA), as a model of triazine dye, and 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CD), as a model of cyclodextrin, were investigated by monitoring the spectral shift that accompanies the binding phenomena. Matrix analysis of the difference spectral titration of CB F3GA with HP-beta-CD revealed only two absorbing species, indicating a host-guest ratio of 1:1. The dissociation constant for this HP-beta-CD-CB F3GA complex, Kd, was found to be 0.43 mM. The data for HP-beta-CD forming inclusion complexes with CB F3GA were used to develop the concept of competitive elution by inclusion complexes in dye-affinity chromatography. When this concept was applied to the elution of L-lactate dehydrogenase from a CB F3GA affinity matrix, it was shown to be an effective elution strategy. It provided a 15-fold purification factor with 89% recovery and sharp elution profile (0.8 column volumes for 80% recovery), which is as good as that obtained by specific elution with NADH (16-fold, 78% recovery and 1.8 column volumes). In addition, the new elution strategy showed a better purification factor and sharper elution profile than traditional non-specific elution with KCl (4.5-fold, and 1.4 column volumes). Hence, competitive elution by inclusion complexes may be a promising strategy for eluting proteins with high recoveries and purification factors in dye-affinity chromatography.

Determination of apparent thermodynamic parameters for adsorption of a midchain peptidyl residue onto a glass surface

Protein adsorption onto the surface of an implanted material is widely recognized as an important factor controlling the biological response. Although numerous studies have been conducted to investigate protein adsorption behavior, very little is actually understood regarding the specific molecular events involved in protein-surface adsorption processes. As a basic science approach to investigate protein-surface interactions, an experimental method is developed and applied to determine apparent thermodynamic parameters for the adsorption of a single midchain peptidyl residue onto a glass surface. This article presents the results of adsorption studies for four molecular weight ranges of poly-L-lysine onto glass microspheres in physiologic saline at four temperatures. Isotherm data plots are constructed and the apparent changes in enthalpy (DeltaH degrees ), entropy (DeltaS degrees ), and Gibbs' free energy (DeltaG degrees ) are calculated assuming a Langmuir-like model for adsorption. Estimates of apparent DeltaH degrees, DeltaS degrees, and DeltaG degrees for the adsorption of a single midchain lysine residue are determined from the initial slopes of the plots of the apparent thermodynamic parameters versus the degree of polymerization of the adsorbed poly-L-lysine. It is proposed that the generation of such molecular-level adsorption data is a necessary step toward the goal of understanding, predicting, and controlling protein-surface interactions.

Interaction of Cibacron blue with polymers: implications for polymer-shielded dye-affinity chromatography of phosphofructokinase from baker's yeast

Interactions between Cibacron Blue F3GA and water-soluble non-ionic polymers were investigated by monitoring the spectral shift that accompanies the binding phenomena. Polyvinylpyrrolidone (PVP) and poly(vinyl alcohol) were the only polymers among those tested found to interact effectively with the dye. The difference spectra for the PVP-dye complex was typical of "electrostatic interaction spectra" at low ionic strength and typical of "hydrophobic interaction spectra" in the presence of 1.5 M KCl. The binding constant and the number of binding sites per polymer molecule were calculated using the simplest model of independent binding sites. One dye molecule was bound by a PVP segment with a molecular mass of 1000-1300. Regardless of the size of the polymer molecules, the binding constants were in the micromolar range. Poly(vinyl alcohol) bound less efficiently to Cibacron Blue than PVP. One dye molecule was bound by a polymer segment with a molecular mass of about 10,000. The data on PVP complexing with Cibacron Blue were used to develop the concept of polymer-shielded dye-affinity chromatography. This concept was successfully applied to the chromatography of phosphofructokinase (EC 2.7.1.11) from baker's yeast. Specific elution of the bound enzyme from PVP-shielded column resulted in an efficient process with 27-fold purification.

Characteristics of spontaneously produced and of virus-induced human LuKII cell interferons

Several human lymphoblastoid cell lines produced significant levels of interferon (IFN) activity in the absence of any IFN induces. We have partially purified spontaneous IFN (SpIFN) from LuKII cells and compared it with the IFN activity produced by the same cells following Sendai virus induction. Virus-induced LuKII IFN reached maximum titers of 1000-6000 reference units/ml at 12 to 15 houts post-induction and produced a heterogeneous electrophoretic profile with major (18,500 dalton) and minor (23,500 dalton) species. Spontaneous LuKII IFN was produced very slowly over several days and reached maximum titers of 100-1000 reference units/ml. Crude SpIFN (25-100 ref. units/ml) was purified to 1-6 X 10(5) ref. units/ml with a 53-80 percent overall recovery, and it consistently migrated as a homogeneous 20,000 dalton band upon SDS gel electrophoresis. Although spontaneously produced and virus-induced lymphoblastoid IFNs differed in their ability to be neutralized by anti-mouse IFN antiserum (18), both types of IFN were only 1 percent cross-reactive on heterologous mouse L cells. We conclude that IFN definitely can be produced by many human lymphoblastoid cell lines in the absence of inducers, and that LuKII SpIFN has different characteristics than the IFNs produced by the same cell line following viral induction. Since it is now known that there are many IFN-alpha genes (3, 10), it seems likely that these cell lines may provide a system for studying the selective expression of one or more of these genes.

Purification of human lymphoblastoid cell-derived interferon-alpha by controlled-pore glass bead adsorption chromatography and molecular sieving

Human lymphoblastoid cell-derived interferon-alpha has been purified by a combination of chromatography on controlled-pore glass 350, gel filtration on Ultrogel AcA 54 and hydrophobic chromatography on Phenyl-Sepharose CL-4B. Specific activities of greater than 10(7) units/mg have been obtained. Controlled-Pore Glass has the advantages of accommodating large volumes of induced medium in an "in-line" process giving high recoveries of interferon and removing most of any contaminating DNA.

Chromatography of human leukocyte interferon on controlled pore glass

Human leukocyte interferon (HuIFN-alpha ) was adsorbed on controlled pore glass (CPG) beads in 0.01 M potassium phosphate, pH 7.2. Partial recovery fo HuIFN-alpha from CPG, ranging from 50% to 75%, was obtained with ethylene glycol (6.8 M), ammonium chloride (1.0 M) and Tris.HCl (1.0 M). A near complete recovery (90%) was obtained with potassium phosphate (1 M), but there was no selectivity in the elution vis á vis other proteins. An efficient elution of HuIFN-alpha was accomplished with tetramethyl-, and tetraethylammonium chlorides: the recovery of HuIFN-alpha was complete at low concentrations (0.25 M to 0.50 M) of these salts at pH 8.0 and the elution of interferon was more selective than with other eluants.