Interaction of thioredoxins with target proteins: Role of particular structural elements and electrostatic properties of thioredoxins in their interplay with 2-oxoacid dehydrogenase complexes

The thioredoxin action upon the 2-oxoacid dehydrogenase complexes is invest igated by using different thioredoxins, both wild-type and mutated. The att acking cysteine residue of thioredoxin is established to be essential for t he thioredoxin-dependent activation of the complexes. Mutation of the burie d cysteine residue to serine is not crucial for the activation, but prevent s inhibition of the complexes, exhibited by the Clamydomonas reinhardtii th ioredoxin m disulfide. Site-directed mutagenesis of D26, W31, F/W12, and Y/ A70 (the Escherichia coli thioredoxin numbering is employed for all the thi oredoxins studied) indicates that both the active site and remote residues of thioredoxin are involved in its interplay with the 2-oxoacid dehydrogena se complexes. Sequences of 11 thioredoxin species tested biochemically are aligned. The thioredoxin residues at the contact between the alpha 3/3(10) and alpha 1 helices, the length of the alpha 1 helix and the charges in the alpha 2-beta 3 and beta 4-beta 5 linkers are found to correlate with the p rotein influence on the 2-oxoacid dehydrogenase complexes (the secondary st ructural elements of thioredoxin are defined according to Eklund H et al., 1991, Proteins 11:13-28). The distribution of the charges on the surface of the thioredoxin molecules is analyzed. The analysis reveals the species sp ecific polarization of the thioredoxin active site surroundings, which corr esponds to the efficiency of the thioredoxin interplay with the 2-oxoacid d ehydrogenase systems. The most effective mitochondrial thioredoxin is chara cterized by the strongest polarization of this area and the highest value o f the electrostatic dipole vector of the molecule. Not only the magnitude, but also the orientation of the dipole vector show correlation with the thi oredoxin action. The dipole direction is found to be significantly influenc ed by the charges of the residues 13/14, 51, and 83/85, which distinguish t he activating and inhibiting thioredoxin disulfides.