Differences in the purification and solution properties of PurC gene products from Streptococcus pneumoniae and Bacillus anthracis
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4-(N-succino)-5-aminoimidazole-4-carboxamide ribonucleotide synthetase (PurC) is a key enzyme in the de novo purine biosynthetic pathway of bacteria and an ideal target pathway for the discovery of antimicrobials. Bacillus anthracis (Ba) and Streptococcus pneumoniae (Sp) are two of the bacteria shown to be severe detriments to public health. To be able to carry out the experimentation that leads to drug discovery, high yields of pure soluble recombinant protein must first be obtained. We studied two recombinant PurC proteins from B. anthracis and S. pneumoniae, using Escherichia coli as the host cells. These two proteins, with very similar amino acid sequences, exhibit very different solution properties, leading to a large difference in yields during protein purification under the same conditions. The yield for SpPurC (>50mG per gram of cells) is ten times greater than that for BaPurC (<5mG per gram of cells). The BaPurC samples in solution consisted of oligomers and dimers, with dimers as its functional form. Comparing the yields of dimers, SpPurC is 25 times greater than that for BaPurC (∼2mG per gram of cell). Our studies suggest that the difference in exposed hydrophobic surface area is responsible for the difference in yields under the same conditions.