Two energetically disparate folding pathways of [alpha]-lytic protease share a single transition state

The Lysobacter enzymogenes α-lytic protease (αLP) is synthesized with a 166 amino acid pro region (Pro) that catalyzes the folding of the 198 amino acid protease into its native conformation. An extraordinary feature of this system is the very high energy barrier (ΔG = 30 kcal mol-1) that effectively prevents αLP from folding in the absence of Pro (t1/2 = 1800 years). A pair of mutations has been isolated in the protease that completely suppresses the catalytic defect incurred in Pro by truncation of its last three amino acids. These mutations also accelerate the folding of αLP in the absence of Pro by 400-fold. An energetic analysis of the two folding reactions indicates that the mutations stabilize the transition states of both the catalyzed and uncatalyzed folding reactions by 3 kcal mol-1 . This finding points to a single transition state for these two distinct and energetically disparate folding pathways, and raises the possibility that all αLP folding pathways share the same transition state.