title: Distribution, transition and thermodynamic stability of protein conformations in the denaturant-induced unfolding of proteins.
abstract: BACKGROUND
  Extensive and intensive studies on the unfolding of proteins require appropriate theoretical model and parameter to clearly illustrate the feature and characteristic of the unfolding system. Over the past several decades, four approaches have been proposed to describe the interaction between proteins and denaturants, but some ambiguity and deviations usually occur in the explanation of the experimental data.
  
  
  RESULTS
  In this work, a theoretical model was presented to show the dependency of the residual activity ratio of the proteins on the molar denaturant concentration. Through the characteristic unfolding parameters ki and Δmi in this model, the distribution, transition and thermodynamic stability of protein conformations during the unfolding process can be quantitatively described. This model was tested with the two-state unfolding of bovine heart cytochrome c and the three-state unfolding of hen egg white lysozyme induced by both guanidine hydrochloride and urea, the four-state unfolding of bovine carbonic anhydrase b induced by guanidine hydrochloride and the unfolding of some other proteins induced by denaturants. The results illustrated that this model could be used accurately to reveal the distribution and transition of protein conformations in the presence of different concentrations of denaturants and to evaluate the unfolding tendency and thermodynamic stability of different conformations. In most denaturant-induced unfolding of proteins, the unfolding became increasingly hard in next transition step and the proteins became more unstable as they attained next successive stable conformation.
  
  
  CONCLUSIONS
  This work presents a useful method for people to study the unfolding of proteins and may be used to describe the unfolding and refolding of other biopolymers induced by denaturants, inducers, etc.
authors.affiliation: College of Life Science, Northwest University, Xi'an, Shaanxi, China.
authors.forename: Liujiao
authors.initials: L
authors.lastname: Bian
authors.affiliation: College of Life Science, Northwest University, Xi'an, Shaanxi, China.
authors.forename: Xu
authors.initials: X
authors.lastname: Ji
mesh_terms: D000818:Animals; D002256:Carbonic Anhydrases / Q000737:chemistry / Q000378:metabolism; D002417:Cattle; D002645:Chickens; D045304:Cytochromes c / Q000737:chemistry / Q000378:metabolism; D019791:Guanidine / Q000494:pharmacology*; D009113:Muramidase / Q000737:chemistry / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism; D011487:Protein Conformation / Q000187:drug effects; D011489:Protein Denaturation / Q000187:drug effects*; D058767:Protein Unfolding / Q000187:drug effects*; D012044:Regression Analysis; D013816:Thermodynamics; D014508:Urea / Q000494:pharmacology*
chemical_list: D014508:Urea; D045304:Cytochromes c; C421864:hen egg lysozyme; D009113:Muramidase; D002256:Carbonic Anhydrases; D019791:Guanidine