Unfolded conformations of alpha-lytic protease are more stable than its native state.
alpha-Lytic protease (alphaLP), an extracellular bacterial protease, is synthesized with a large amino-terminal pro-region that is essential for its folding in vivo and in vitro. In the absence of the pro-region, the protease folds to an inactive, partially folded state, designated 'I'. The pro-region catalyses protease folding by directly stabilizing the folding transition state (>26kcal mol(-1)) which separates the native state 'N' from I. Although a basic tenet of protein folding is that the native state of a protein is at the minimum free energy, we show here that both the I and fully unfolded states of alphaLP are lower in free energy than the native state. Native alphaLP is thus metastable: its apparent stability derives from a large barrier to unfolding. Consequently, the evolution of alphaLP has been distinct from most other proteins: it has not been constrained by the free-energy difference between the native and unfolded states, but instead by the size of its unfolding barrier.
Sohl
J L
JL
Graduate Group in Biophysics, Howard Hughes Medical Institute, University of California at San Francisco, 94143-0448, USA.
Jaswal
S S
SS
Agard
D A
DA
D004795:Enzyme Stability; D019143:Evolution, Molecular; D011487:Protein Conformation; D017510:Protein Folding; D012697:Serine Endopeptidases / Q000737:chemistry* / Q000235:genetics; D013816:Thermodynamics
D012697:Serine Endopeptidases; C021826:myxobacter alpha-lytic proteinase