title: The native conformation of plasmepsin II is kinetically trapped at neutral pH.
abstract: Plasmepsin II (PMII), an aspartic protease from the malarial parasite Plasmodium falciparum, represents a model for understanding protease structure/function relationships due to its unique structure and properties. The present study undertook a thermodynamic and kinetic analysis of the PMII folding mechanism and a pH stability profile. Differential scanning calorimetry revealed that the native state of PMII (Np) was irreversibly unfolded, and in the pH range of 6.5-8.0, PMII refolds to a denatured state (Rp) with higher thermal stability than Np. Rp could also be formed upon partially unfolding PMII at pH 11.0 and 37 °C for 2h, followed by adjustment to a pH in the range of 6.5-8.0. While Rp could be folded/unfolded reversibly, Np was shown to exist as a kinetically trapped state. By examining the unfolding kinetics of Np and the kinetics of Rp folding to Np at 25 °C, it was found that Np is kinetically trapped by an unfolding barrier of 25.5 kcal/mol, and yet once unfolded, is prevented from folding by a comparable folding barrier. The folding mechanism of PMII is similar to that reported for pepsin. It is hypothesized that the PMII zymogen also utilizes a prosegment-catalyzed folding mechanism.
authors.affiliation: Department of Food Science, University of Guelph, Guelph, Ontario, Canada N1G2W1.
authors.forename: Huogen
authors.initials: H
authors.lastname: Xiao
authors.forename: Derek
authors.initials: D
authors.lastname: Dee
authors.forename: Rickey Y
authors.initials: RY
authors.lastname: Yada
mesh_terms: D016282:Aspartic Acid Endopeptidases / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D002942:Circular Dichroism; D004795:Enzyme Stability; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010434:Pepsin A / Q000737:chemistry; D010963:Plasmodium falciparum / Q000201:enzymology; D011487:Protein Conformation; D011489:Protein Denaturation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D015800:Protozoan Proteins / Q000737:chemistry*; D011994:Recombinant Proteins / Q000737:chemistry; D013816:Thermodynamics
chemical_list: D015800:Protozoan Proteins; D011994:Recombinant Proteins; D016282:Aspartic Acid Endopeptidases; D010434:Pepsin A; C100637:plasmepsin II