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The HPr proteins were characterized as folding by a two -state folding mechanism . Here , we present a comparison of the equilibrium and kinetic folding for the HPr protein from Bacillus subtilis , E coli and a key variant from these proteins . For the wild -type protein we find that GHX is greater than GUDC , suggesting that the HPr does not fold by a simple two -state mechanism . This discrepancy is revealed by testing the two -state nature of the folding reaction of HPr with mutation . We show that removing a single charge side chain (Asp 69 ) converts the HPr protein back to a simple two -state mechanism .
Ribonuclease Sa and two charge -reversal variants can be converted into amyloidin vitro by the addition of 2 ,2 ,2 -triflouroethanol (TFE ) . We report here amyloid fibril formation for these proteins as a function of pH . The pH at maximal fibril formation correlates with the pH dependence of protein solubility , but not with stability , for these variants . Additionally , we show that the pH at maximal fibril formation for a number of ivwell -characterized proteins is near the pI , where the protein is expected to be the least soluble . This suggests that protein solubility is an important determinant of fibril formation . |
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