Affinity chromatography in purification of A1 adenosine receptors

Purification and characterization of the human adenosine A(2a) receptor functionally expressed in Escherichia coli

The adenosine A(2a) receptor belongs to the seven transmembrane helix G-protein-coupled receptor family, is abundant in striatum, vasculature and platelets and is involved in several physiological processes such as blood pressure regulation and protection of cells during anoxia. For structural and biophysical studies we have expressed the human adenosine A(2a) receptor (hA2aR) at high levels inserted into the Escherichia coli inner membrane, and established a purification scheme. Expression was in fusion with the periplasmic maltose-binding protein to levels of 10-20 nmol of receptor per L of culture, as detected with the specific antagonist ligand [(3)H]ZM241385. As the receptor C-terminus was proteolyzed upon solubilization, a protease-resistant but still functional receptor was created by truncation to Ala316. Addition of the sterol, cholesteryl hemisuccinate, allowed a stable preparation of functional hA2aR solubilized in dodecylmaltoside to be obtained, and, increased the stability of the receptor solubilized in other alkylmaltosides. Purification to homogeneity was achieved in three steps, including ligand affinity chromatography based on the antagonist xanthine amine congener. The purified hA2aR fusion protein bound [(3)H]ZM241385 with a K(d) of 0.19 nm and an average B(max) of 13.7 nmol x mg(-1) that suggests 100% functionality. Agonist affinities for the purified solubilized receptor were higher than those for the membrane-bound form. Sufficient pure, functional hA2aR can now be prepared regularly for structural studies.

Separation of G structures formed by a 27-mer guanosine-rich oligodeoxyribonucleotide by dye-ligand affinity chromatography

G-DNA structures, formed by a 27-mer guanosine-rich oligodeoxyribonucleotide, AACCCGGCGTTCGGGGGGTACCGGGTT, were isolated and studied by dye-ligand affinity chromatography, using a Reactive Green 19-agarose resin (RG19-aga) and gel electrophoresis. The experiments were performed in the presence of Li+, Na+ and K+, which are able to stabilise the G structures to different extents. Desalting procedures followed by affinity chromatography, performed in the presence of Li+, gave us information on the relationships among the species isolated and their stability. The results show that the more stable species were those obtained in the presence of K+, while in the presence of Li+, the formation of G structures was negligible and the oligonucleotide was almost exclusively present as a stem-loop structure recognised by the RG19-aga affinity resin. Electrophoretic and denaturation and renaturation experiments supported the affinity chromatography results.

Purification of trypsin by affinity chromatography with sulphamethoxazolum ligand

Pharmaceuticals have already been studied comprehensively both in their physico-chemical properties and their biological effect. Most of these compounds are chemically synthesized and less susceptible to degradation by micro-organism or suffering from solvent effect compared with the bio-active substances. Affinity chromatographic columns composed of pharmaceutical compounds as the ligand should have advantages such as long life, low cost and low toxicity. This paper describes the preparation of sulphamethoxazolum immobilized on silica as the column packing and the study of its interactions with proteins and enzymes. It was found that this material showed an affinity specific to trypsin with a dissociation constant of around 10(-6) M. The enzymatic activity of commercial trypsin can be increased by a factor of ten after purification with such a column.