Self-association of adrenodoxin studied by using analytical ultracentrifugation.
The mitochondrial steroid hydroxylase system of vertebrates utilizes adrenodoxin (Adx), a small iron-sulfur cluster protein of about 14 kDa as an electron carrier between a reductase and cytochrome P450. Although the crystal structure of this protein has been elucidated, the solution structure of Adx was discussed contrary in the literature [I.A. Pikuleva, K. Tesh, M.R. Waterman, Y. Kim, The tertiary structure of full-length bovine adrenodoxin suggests functional dimers, Arch. Biochem. Biophys. 373 (2000) 44-55; D. Beilke, R. Weiss, F. Löhr, P. Pristovsek, F. Hannemann, R. Bernhardt, H. Rüterjans, A new electron mechanism in mitochondrial steroid hydroxylase systems based on structural changes upon the reduction of adrenodoxin, Biochemistry 41 (2002) 7969-7978]. Therefore, it was necessary to study the self-association of this protein by using analytical ultracentrifugation over a larger concentration range. As could be demonstrated in sedimentation velocity experiments, as well as sedimentation equilibrium runs with explicit consideration of thermodynamic non-ideality, the full-length protein (residues 1-128) in the oxidized state resulted in a monomer-dimer equilibrium (K(a) approximately 3 x 10(2) M(-1)). For truncated Adx (1-108), as well as the reduced Adx, the association behavior was strongly reduced. The consequences of this behavior are discussed with respect to the physiological meaning for the Adx system.
Behlke
Joachim
J
Max Delbrück Center for Molecular Medicine, 13092 Berlin, FRG. behlke@mdc-berlin.de
Ristau
Otto
O
Müller
Eva-Christina
EC
Hannemann
Frank
F
Bernhardt
Rita
R
D000325:Adrenodoxin / Q000737:chemistry*; D010084:Oxidation-Reduction; D020836:Protein Structure, Quaternary; D013816:Thermodynamics; D014461:Ultracentrifugation / Q000379:methods
D000325:Adrenodoxin