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Published on: September 8, 2009
The alkali molten globule state of ferrocytochrome c: extraordinary stability, persistent structure, and constrained
D Krishna Rao1, Rajesh Kumar, M Yadaiah
1School of Chemistry, University of Hyderabad, Hyderabad 500046, India.
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.
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