Figure 3

pH induced compaction of EhPSAT, oligomeric state and thermal stability. (A) Curves 1-4 represent SEC profile of EhPSAT on a superdex 200, 10/300 GL column at pH 6, 7, 8 and 9, respectively. The inset shows the graph of elution volume plotted against standard molecular mass markers. The proteins are (1) 440 KDa (ferritin), (2)158 KDa (aldolase), (3) 75 KDa (conalbumin) and (4) 43 KDa (ovalbumin). (B) 10% SDS-PAGE profile of glutaraldehyde crosslinked sample of EhPSAT incubated at different pH. Lane 1-6 represent molecular weight markers, uncrosslinked EhPSAT, and glutaraldehyde crosslinked form of EhPSAT at pH 9, 8, 7 and 6, respectively. Cooperative thermal unfolding of EhPSAT at pH 8.5 (panel C) and 6 (panel D) as measured by loss of CD ellepticity at 222 nm and 415 nm. A linear extrapolation of baselines in pre and post transition regions was used to determine the fraction unfolded protein within the transition region by assuming a two state mechanism of unfolding. The open and filled circle represent for far and near UV-CD signals, respectively. The thermal transition of the enzyme was found to be irreversible with precipitation observed at the end of the scan.