Hydrophobic interaction chromatography of proteins and peptides on spheron P-300

An active wound dressing for controlled convective mass transfer with the wound bed

Conventional wound dressings-gauze, plastic films, foams, and gels-do not allow for spatial and temporal control of the soluble chemistry within the wound bed, and are thus limited to a passive role in wound healing. Here, we present an active wound dressing (AWD) designed to control convective mass transfer with the wound bed; this mass transfer provides a means to tailor and monitor the chemical state of a wound and, potentially, to aid the healing process. We form this AWD as a bilayer of porous poly(hydroxyethyl methacrylate) (pHEMA) and silicone; the pHEMA acts as the interface with the wound bed, and a layer of silicone provides a vapor barrier and a support for connecting to external reservoirs and pumps. We measure the convective permeability of the pHEMA sponge, and use this value to design a device with a spatially uniform flow profile. We quantify the global coefficient of mass transfer of the AWD on a dissolvable synthetic surface, and compare it to existing theories of mass transfer in porous media. We also operate the AWD on model wound beds made of calcium alginate gel to demonstrate extraction and delivery of low molecular weight solutes and a model protein. Using this system, we demonstrate both uniform mass transfer over the entire wound bed and patterned mass transfer in three spatially distinct regions. Finally, we discuss opportunities and challenges for the clinical application of this design of an AWD.

Hydrophobic interaction chromatography of proteins IV

Adsorption of proteins on surfaces of hydrophobic interaction chromatography media is at least a two-stage process. Application of pure protein pulses (bovine serum albumin and beta-lactoglobulin) to hydrophobic interaction chromatography media yielded two chromatographic peaks at low salt concentrations. At these salt concentrations, the adsorption process is affected by a second reaction, which can be interpreted as protein spreading or partial unfolding of the protein. The kinetic constants of the spreading reaction were derived from pulse response experiments at different residence times and varying concentrations by applying a modified adsorption model considering conformational changes. The obtained parameters were used to calculate uptake and breakthrough curves for spreading proteins. Although these parameters were determined at low saturation of the column, predictions of overloaded situations could match the experimental runs satisfactorily. Our findings suggest that proteins which are sensitive to conformational changes should be loaded at high salt concentrations in order to accelerate the adsorption reaction and to obtain steeper breakthrough curves.

Protein instability during HIC: Hydrogen exchange labeling analysis and a framework for describing mobile and stationary phase effects

Unfolding of marginally stable proteins is a significant factor in commercial application of hydrophobic interaction chromatography (HIC). In this work, hydrogen-deuterium isotope exchange labeling has been used to monitor protein unfolding on HIC media for different stationary phase hydrophobicities and as a function of ammonium sulfate concentration. Circular dichroism and Raman spectroscopy were also used to characterize the structural perturbations experienced by solution phase protein that had been exposed to media and by protein adsorbed on media. As expected, greater instability is seen on chromatographic media with greater apparent hydrophobicity. However, increased salt concentrations also led to more unfolding, despite the well-known stabilizing effect of ammonium sulfate in solution. A thermodynamic framework is proposed to account for the effects of salt on both adsorption and stability during hydrophobic chromatography. Using appropriate estimates of input quantities, analysis with the framework can explain how salt effects on stability in chromatographic systems may contrast with solution stability.

Analysis of pH-dependent protein interactions with gel filtration medium

A prepacked Superose 12 HR 10/30 column was used to study the effects of elution ionic strength and pH on the chromatographic behaviour of a strong hydrophobic Clostridium thermocellum endoglucanase (1) and two weak hydrophobic proteins, Clostridium thermocellum endoglucanase C and egg white lysozyme. Ion-exclusion or ion-exchange interactions between weakly hydrophobic proteins and the gel matrix were observed at low ionic strength, depending on whether the pH of the elution buffer was higher or lower than the pI values of the proteins. These interactions were due to the presence of negatively charged groups on the surface of Superose and could be eliminated at any pH by adding electrolyte at a concentration determined by its chemical identity. The optimum results were observed with sodium sulphate at a concentration of 100 mM. The chromatographic behaviour of strong hydrophobic endoglucanase (1) on a Superose column as a function of pH was much more complex because of two interplaying effects, electrostatic and hydrophobic. Ideal size-exclusion chromatography could be achieved only in a narrow range of the conditions: first, the mobile phase must contain a weak salting-out electrolyte such as NaCl, and second, the mobile phase pH must be high enough that hydrophobic interactions between the solute and support are balanced by their electrostatic repulsion. At pH greater than pI, the retardation of endoglucanase (1) gradually increased with decreasing pH as a result of lowering of repulsive electrostatic interactions whether or not the buffer ionic strength was high. At pH less than pI a drastic increase in the capacity factor k' was observed owing to the additivity of hydrophobic and ion-exchange effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Rapid desalting of ammonium sulfate solutions by hydrophobic interaction chromatography

Open-air hydrophobic interaction chromatography with alkyl carbon functional groups coupled to agarose beads has been used to desalt large volumes of ammonium sulfate-fractionated bacterial cell lysates. The protein of interest can be simultaneously desalted and concentrated in less than 4 h, and the yield is significantly better than that obtained by the standard technique of precipitation, centrifugation, and dialysis.

Hydrophobic interaction chromatography of proteins on Separon hema. I. The effect of an initial salt concentration on the separation of proteins

The influence of an initial salt concentration, phi(0), on the gradient separation of proteins using hydrophobic interaction chromatography on Separon HEMA 1000 was investigated. The results obtained were compared with the retention times and peak widths calculated according to a mathematical model.

Effects of solutions used for storage of size-exclusion columns on subsequent chromatography of peptides and proteins

The effects of storage of size-exclusion column packing materials in methanolic or azide-water solutions on subsequent separations were tested. Three commercially available columns were used in these studies; the Toyo-Soda Bio-Sil TSK 125, Bio-Sil TSK 250 and the DuPont Bio-Series GF-250. Upon initial chromatography, all three columns bound up to 760 micrograms of cytochrome c tryptic peptides. Sample binding to packing material is probably a function of the positively charged basic groups on peptides or proteins interacting with silanol groups. The larger the peptide, the less the opportunity for silanol-charged group interaction, hence, less binding. Initial samples introduced to a new column occupy the binding sites. Equilibration with neat methanol removes the bound protein revealing sites which bind sample. After absorption of peptides to binding sites on the packing material, storage in neat methanol regenerates the binding sites. Storage in 10% methanol diminished the binding phenomenon, but storage in azide-water reduced binding to a range below detection at the microgram level. Our recommendation to users of size-exclusion chromatographic columns is that one satisfy the absorption capacity of a new column by injecting a sufficient quantity of a basic peptide standard or other convenient sample to reduce available binding sites before using the column for important separations. Store columns in azide-water or 10% methanol to prevent the regeneration of exposed silanol groups.

Model study of hydrophobic interactions of alpha- and beta-trypsin and alpha-chymotrypsin

The hydrophobic interactions of alpha- and beta-trypsin as a function of ionic strength and pH were studied by hydrophobic chromatography. Evidence was obtained that in spite of the identical specificities and similar activities of alpha- and beta-trypsin, the cleavage of the Lys-Ser bond induces conformational changes in the neighbourhood of the active site. Over a wide range of pH and salt concentration the non-polar residues on the surface of the molecule of beta-trypsin are more exposed to an external environment than on the molecule of alpha-trypsin. In the trypsin(chymotrypsin)-inhibitor complexes the majority of hydrophobic amino acids are buried; other hydrophobic residues localized on the surface contribute only very slightly to the interaction with the chromatographic support. The retention of trypsin, chymotrypsin and their diisopropylphosphoryl derivatives on a support with flexible hydrophobic ligands bonded to the matrix through a spacer (octyl-Sepharose) was correlated with the retention on a support with hydrophobic binding sites incorporated into the rigid matrix of the resin (Spheron). The native enzymes are always more retained; this indicates that the substitution results in the shielding of the non-polar residues in the neighbourhood of the active site. The differences in the slope of individual proteins, resulting from the correlation of the retention values obtained with both supports at several sodium chloride concentrations are explained by differences in the accessibility of the surface non-polar residues in the individual proteins. In experiments with model peptides the contribution of the individual hydrophobic amino acids to the retention was investigated.

Isolation of human haemopexin by bioaffinity chromatography on haeme-sepharose

A preparative procedure was developed for the isolation of human apohaemopexin from Cohn fraction IV or blood serum, based on bioaffinity chromatography on haeme-Sepharose. The isolation is carried out in the pH range 4-8; hence the possibility of degradation of the carbohydrate moiety of the glycoprotein in the acidic media used in other isolation procedures is decreased. Owing to the conditions of the separation and the good stability of the affinity support, the column can be used repeatedly for long periods without a significant loss of binding capacity. The reversibility of the conformational changes that haemopexin undergoes in acidic media was examined by hydrophobic chromatography. The original hydrophobic characteristics were restored only approximately 48 h after haemopexin had been brought into a neutral medium.

Separation of oligonucleotides on ion-exchange derivatives of Spheron

Diphenylamine-formic acid hydrolyzate of Bacillus subtilis DNA (a mixture of pyrimidine oligodeoxyribonucleotides) was chromatographed using an ionic strength gradient on seven ion exchangers: five DEAE-Spherons 300 of various capacities, two types of BD-Spheron 300 and DEAE-Sephadex A-25. The suitability of ion-exchange derivatives of Spheron for the chromatography of oligonucleotides is discussed. The separation of mono- to undeca-deoxyribonucleotides was achieved.