title: Statistical Mechanical Model for pH-Induced Protein Folding: Application to Apomyoglobin.
abstract: Despite the major role of pH in protein folding and stability, a quantitative understanding of the pH-induced protein folding mechanism remains elusive. Two conventional models, the Monod-Wyman-Changeux and Linderstrøm-Lang smeared charge models, respectively, have been used to analyze the formation/disruption of specific native structures and fluctuating non-native states. However, there are only a few models that can represent the overall kinetic events of folding/unfolding independent of the properties of relevant molecular species, which has hampered the efforts to systematically analyze pH-induced folding. Here, we constructed a statistical mechanical model that incorporates the protonation mechanism of conventional models along with a combined manual search and least-squares fitting procedure, which was used to investigate the folding of horse apomyoglobin over a wide pH range (2.2-6.7), with a time window ranging from ∼40 μs to ∼100 s, using continuous-/stopped-flow fluorescence at 8 °C. Quantitative analysis assuming a five-state sequential scheme indicated that (1) pH-induced folding/unfolding is represented by both specific binding and Coulombic interactions; (2) kinetic folding/unfolding intermediates share kinetic mechanisms with the equilibrium intermediate, indicating their equivalence; and (3) native-like properties are acquired successively during folding by intermediates and in transition states. This model could also be applied to a variety of association/dissociation processes.
authors.affiliation: Graduate School of Science, Nagoya University , Furo-cho, Chikusa, Nagoya, Aichi 464-8602, Japan.
authors.forename: Takuya
authors.initials: T
authors.lastname: Mizukami
authors.affiliation: Graduate School of Science, Nagoya University , Furo-cho, Chikusa, Nagoya, Aichi 464-8602, Japan.
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Sakuma
authors.affiliation: Graduate School of Science, Nagoya University , Furo-cho, Chikusa, Nagoya, Aichi 464-8602, Japan.
authors.forename: Kosuke
authors.initials: K
authors.lastname: Maki
mesh_terms: D000818:Animals; D001059:Apoproteins / Q000737:chemistry* / Q000378:metabolism; D006736:Horses; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008958:Models, Molecular; D015233:Models, Statistical; D009211:Myoglobin / Q000737:chemistry* / Q000378:metabolism; D017510:Protein Folding
chemical_list: D001059:Apoproteins; D009211:Myoglobin; C010857:apomyoglobin