Additional file 6.

Expression, oligomerization and folding of LrpA1. Heterologous expression of the His6-tagged H. salinarum LrpA1 in E. coli BL21(DE3) and protein purification analyzed by SDS-PAGE. E. coli extracts before induction (lane 1), two and three hours after induction with 0.6 mM IPTG (lane 2, 3) and purified protein, displayed by an arrow (lane 4-6) (A). After dialysis against a high salt buffer correct folding of LrpA1 was proved by CD-spectroscopy, were 56% α-helices, 11% β-sheet, 14% β-turn and 24% random coil structure was determined (B). The theoretical calculated values for LrpA1 are 42% α-helices, 27% β-sheet and 31% random coil structure was determined. Folded LrpA1 in high salt has a predominant α-helical structure. An aberrance of ~10% between the measured and the theoretical value is in the range of error and has been shown in previous studies [60] (B). The size exclusion chromatography elution profile showed dimerisation of LrpA1 after renaturation (C). Calibration standards used for this run are indicated in additional table S2 (C). LrpA1 elutes at a volume of 1.32 ml which is a corresponding molecular weight 31.1 kDa showing a LrpA1 dimer. The theoretical size of a LrpA1 monomer is 15.2 kDa.

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Schwaiger et al. BMC Molecular Biology 2010 11:40   doi:10.1186/1471-2199-11-40