title: Pressure equilibrium and jump study on unfolding of 23-kDa protein from spinach photosystem II.
abstract: Pressure-induced unfolding of 23-kDa protein from spinach photosystem II has been systematically investigated at various experimental conditions. Thermodynamic equilibrium studies indicate that the protein is very sensitive to pressure. At 20 degrees C and pH 5.5, 23-kDa protein shows a reversible two-state unfolding transition under pressure with a midpoint near 160 MPa, which is much lower than most natural proteins studied to date. The free energy (DeltaG(u)) and volume change (DeltaV(u)) for the unfolding are 5.9 kcal/mol and -160 ml/mol, respectively. It was found that NaCl and sucrose significantly stabilize the protein from unfolding and the stabilization is associated not only with an increase in DeltaG(u) but also with a decrease in DeltaV(u). The pressure-jump studies of 23-kDa protein reveal a negative activation volume for unfolding (-66.2 ml/mol) and a positive activation volume for refolding (84.1 ml/mol), indicating that, in terms of system volume, the protein transition state lies between the folded and unfolded states. Examination of the temperature effect on the unfolding kinetics indicates that the thermal expansibility of the transition state and the unfolded state of 23-kDa protein are closer to each other and they are larger than that of the native state. The diverse pressure-refolding pathways of 23-kDa protein in some conditions were revealed in pressure-jump kinetics.
authors.affiliation: Key Laboratory of Proteomics, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, the Chinese Academy of Sciences, Shanghai, China.
authors.forename: Cui-Yan
authors.initials: CY
authors.lastname: Tan
authors.forename: Chun-He
authors.initials: CH
authors.lastname: Xu
authors.forename: Jun
authors.initials: J
authors.lastname: Wong
authors.forename: Jian-Ren
authors.initials: JR
authors.lastname: Shen
authors.forename: Shinsuke
authors.initials: S
authors.lastname: Sakuma
authors.forename: Yasusi
authors.initials: Y
authors.lastname: Yamamoto
authors.forename: Reinhard
authors.initials: R
authors.lastname: Lange
authors.forename: Claude
authors.initials: C
authors.lastname: Balny
authors.forename: Kang-Cheng
authors.initials: KC
authors.lastname: Ruan
mesh_terms: D003198:Computer Simulation; D007700:Kinetics; D008956:Models, Chemical; D008970:Molecular Weight; D045332:Photosystem II Protein Complex / Q000032:analysis / Q000737:chemistry*; D011312:Pressure; D011489:Protein Denaturation; D017510:Protein Folding; D018724:Spinacia oleracea / Q000378:metabolism*; D013696:Temperature
chemical_list: D045332:Photosystem II Protein Complex