✍ Scribed by Jonas Carlsson; Klaus Mosbach; Leif Bülow
No coin nor oath required. For personal study only.
Proteins carrying genetically attached polyhistidine tails have been purified using affinity precipitation with metal chelates. DNA fragments encoding four or five histidine residues have been genetically fused to the oligomeric enzymes lactate dehydrogenase (Bacillus stearother- mophilus), 0-glucoronidase (Escherichia cold, and galactose dehydrogenase (Pseudomonas fluorescens) as well as to the monomeric protein A (Staphylococcus aureus). The chimeric genes were subsequently expressed in f. coli. The engineered enzymes were successfully purified from crude protein solutions using ethylene glycolbis (P-aminoethyl) tetraacetic acid (EGTA) charged with Zn2+ as precipitant, whereas protein A, carrying only one attached histidine tail, did not precipitate. However, all of the engineered proteins could be purified on immobilized metal affinity chromatography (IMAC) columns loaded with Zn2+. The potential of using the same histidine tails for site-specific immobilization of proteins was also investigated. The enzymes were all catalytically active when immobilized on IMAC gels. For instance, immobilized lactate dehydrogenase, carrying tails composed of four histi- dine residues, displaced 83% of the soluble enzyme activity.
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