title: The alkali molten globule state of ferrocytochrome c: extraordinary stability, persistent structure, and constrained overall dynamics.
abstract: This paper describes the structural and dynamic properties of a hitherto uncovered alkali molten globule (MG) state of horse "ferrocytochrome c" (ferrocyt c). Several experimental difficulties mainly because of heme autoxidation and extraordinary stability of ferrocyt c have been overcome by working with the carbonmonoxide-bound molecule under extremely basic condition (pH 13) in a strictly anaerobic atmosphere. Structural and molecular properties extracted from basic spectroscopic experiments suggest that cations drive the base-denatured CO-liganded protein to the MG state. The stability of this state is approximately 5.2 kcal mol(-)(1), and the guanidinium-induced unfolding transition is sharp (m(g) approximately 2.3 kcal mol(-)(1) M(-)(1)), suggesting contents of rigid tertiary structure. Strategic experiments involving the measurement of the CO association rate to the base-denatured protein and intrachain diffusion rates measured by laser photolysis of CO indicate a substantially restricted overall motion and stiffness of the polypeptide chain in the MG state. Possible placement of the state in the folding coordinate of ferrocyt c is discussed.
authors.affiliation: School of Chemistry, University of Hyderabad, Hyderabad 500046, India.
authors.forename: D Krishna
authors.initials: DK
authors.lastname: Rao
authors.forename: Rajesh
authors.initials: R
authors.lastname: Kumar
authors.forename: M
authors.initials: M
authors.lastname: Yadaiah
authors.forename: Abani K
authors.initials: AK
authors.lastname: Bhuyan
mesh_terms: D000468:Alkalies / Q000737:chemistry* / Q000378:metabolism; D002248:Carbon Monoxide / Q000737:chemistry / Q000378:metabolism; D002942:Circular Dichroism; D045304:Cytochromes c / Q000737:chemistry* / Q000378:metabolism; D004795:Enzyme Stability; D019791:Guanidine / Q000378:metabolism / Q000494:pharmacology; D007700:Kinetics; D008968:Molecular Conformation; D010782:Photolysis; D011489:Protein Denaturation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012965:Sodium Chloride / Q000378:metabolism / Q000494:pharmacology; D013056:Spectrophotometry, Ultraviolet
chemical_list: D000468:Alkalies; D012965:Sodium Chloride; D002248:Carbon Monoxide; D045304:Cytochromes c; D019791:Guanidine