Streptavidin and its variants were produced by cytoplasmic expression in E. coli in inclusion bodies. After stabilization and refolding of the functional tetrameric and monomeric variants, purification was carried out by ammonium sulfate precipitation, Ion Exchange Chromatography and size exclusion chromatography. Samples of each required step were analysed by SDS-PAGE. Finally each of the successfully purified variants were characterized. Mass spectrometry was used to confirm the expected size, circular dichroism spectroscopy (cd) to determine folding states, fluorescence titration and surface plasmon resonance for determining binding affinities.

Results can be seen in Table 1.

All cd spectra were evaluated by Spectra Manager Software and results can be seen in figure 1.

Figure 1: Distribution of secondary structure elements for each protein.