title: Compressibility changes accompanying conformational transitions of apomyoglobin.
abstract: We used high-precision density and ultrasonic velocity measurements to characterize the native (N), molten globule (MG), and unfolded (U) conformations of apomyoglobin. The molten globule states that were studied in this work include the MG(pH4)(NaCl) state observed at pH 4 and 20 mM NaCl, the MG(pH4)(NaTCA) state observed at pH 4 and 20 mM sodium trichloracetate (NaTCA), the MG(pH2)(NaCl) state observed at pH 2 and 200 mM NaCl, and the MG(pH2)(NaTCA) state observed at pH 2 and 20 mM NaTCA. We used our densimetric and acoustic data to evaluate changes in adiabatic compressibility associated with the acid- or salt-induced N-to-MG, MG-to-U, MG-to-MG, and U-to-MG transitions of the protein. The N-to-MG(pH4)(NaCl) and N-to-MG(pH4)(NaTCA) transitions are accompanied by decreases in compressibility of -(3.0 +/- 0.6) x 10(-6) and -(2.0 +/- 0.6) x 10(-6) cm3 g(-1)bar(-1), respectively. The N-to-MG(pH2)(NaCl) and N-to-MG(pH2)(NaTCA) transitions are associated with compressibility changes of -(4.9 +/- 1.1) x 10(-6) and (0.7 +/- 0.9) x 10(-6) cm3 g(-1) bar(-1), respectively. We interpret these data in terms of the degree of unfolding of the various molten globule forms of apomyoglobin. In general, our compressibility data reveal significant disparities between the various equilibrium molten globule states of apomyoglobin while also quantitatively characterizing each of these states. Volumetric insights provided by our data facilitate gaining a better understanding of the folding pathways, intermediates, and kinetics of apomyoglobin folding.
authors.affiliation: Department of Pharmaceutical Sciences, Leslie Dan Facultyof Pharmacy, University of Toronto, 19 Russell Street, Toronto, Ontario M5S 2S2, Canada.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Taulier
authors.forename: Irina V
authors.initials: IV
authors.lastname: Beletskaya
authors.forename: Tigran V
authors.initials: TV
authors.lastname: Chalikian
mesh_terms: D000818:Animals; D001059:Apoproteins / Q000737:chemistry*; D019245:Compressive Strength; D006736:Horses; D009211:Myoglobin / Q000737:chemistry*; D011312:Pressure; D011487:Protein Conformation; D017510:Protein Folding; D013053:Spectrophotometry; D014465:Ultrasonics; D014867:Water / Q000737:chemistry
chemical_list: D001059:Apoproteins; D009211:Myoglobin; C010857:apomyoglobin; D014867:Water