Affinity chromatography of fibroblast growth factors on substituted polystyrene

Randomness and biospecificity: random copolymers are capable of biospecific molecular recognition in living systems

Biospecific molecular recognition in living systems is known to be based on the lock and key principle as proposed by Emil Fischer. Based on this concept, biospecific polymers have been produced synthetically by attaching biospecific 'keys' to the polymer chain. We postulate that biospecificity can be achieved by alternative means, namely random substitution of a preformed polymer with suitable chemical groups or random copolymerization of suitable functional monomers. Such polymers, we suggest, will contain arrangements of the chemical functions which mimic natural biospecific sites and the probability of occurrence of such arrangements will depend on the average composition of the polymer. In support of this principle, we have developed several functional random copolymer systems which possess a variety of biological properties depending on the type of chemical function. Examples are: polymers possessing anticoagulant properties similar to those of heparin; polymers which interact specifically with components of the immune system; and polymers which, in contact with cells, affect their growth and metabolism. In the case of statistical copolymers possessing 'DNA-like' properties obtained by phosphorylation of hydroxylated polystyrene derivatives, Monte Carlo simulations were used to determine the distribution of phosphodiester (PDE) groups along the chains and to compute the probabilities of occurrence of particular arrangements of PDE found in the 'DNA-like' sites. The results showed that these sites are made up of PDE groups separated by distances that closely match those between the same groups along a generatrix of the DNA double-helix cylinder. These findings offer the prospect of manufacturing polymeric biomaterials endowed with biomimetic character. Moreover, they provide the basis for a hypothesis regarding the appearance of biospecificity at the origin of life, suggesting that biospecific structures may have evolved by natural selection from purely random copolymers. It is likely therefore that biospecificity is a continuous function of randomness, arising from purely statistical distributions of reactivity and evolving into precisely defined structures such as those involved in ligand-receptor interactions.

Affinity chromatography of fibroblast growth factors on coated silica supports grafted with heparin

Dextran-coated silica beads are excellent supports for affinity chromatography of proteins. They can be easily grafted using conventional coupling methods with different active ligands, such as heparin. Fibroblast growth factors develop specific interactions with heparin through well-defined amino acids sequences. The heparin-dextran coated silica phases exhibit an affinity for these growth factors. Under our experimental conditions, the basic form can be absorbed on the solid support at a moderate salt concentration (0.5 M sodium chloride) and can be selectively desorbed by increasing the ionic strength of the eluent. The purification performances of such phases are compared to those obtained on the heparin grafted soft gels. Because of their mechanical properties, the dextran-coated silica supports were also used in high-performance affinity chromatography to purify fibroblast growth factors from a bovine brain crude extract.

High-performance affinity chromatography of basic fibroblast growth factor on polystyrene sulphonate resins modified with serine

Basic fibroblast growth factor (bFGF) is a heparin-binding growth factor, so it was usually purified by affinity chromatography on a heparin-grafted support. It was previously observed that, among several modified polystyrene that exhibit anticoagulant heparin-like properties, insoluble polystyrenes modified by chlorosulphonation substituted with serine (PSSer) develop specific interactions with bFGF in solution. These PSSer resins were used as stationary phases in high-performance affinity chromatography in order to separate the radiolabelled growth factor from a bovine brain crude extract. The growth factor is strongly bound to the solid phase, as demonstrated by the adsorption isotherms. It can be adsorbed on the resin at low ionic strength and be desorbed by raising the salt concentration in the eluent. The effects of flow-rate, of the initial buffer and of the slope of the salt gradient on the adsorption and on the desorption of bFGF were investigated in order to study the thermodynamic and the kinetic parameters of the interactions and to define the optimum conditions for a fast and efficient separation of the growth factor.