Quantitative protein stability measurement in living bacteria
Hydrogen exchange detected by MALDI mass spectrometry was used to measure the thermodynamic stability of proteins. The stability of the N-terminal domain measured in vitro, qualitatively correlated with its degradation because the folding kinetics of the protein was in rapid pre-equilibrium relative to its proteolysis. Some of the hydrogen atoms in peptides and proteins were labile to exchange with the surrounding solvent and a number of these exchangeable hydrogens were protected by the native conformation of the protein. The results show that the measured in vivo stability is 6.7 ± 0.13 kcal/mol and the in vitro stability of the protein obtained by performing H/D exchange on lysed bacteria at pH 8 is 6.7 ± 0.2 kcal/mol.