Solution structure of the lipoyl domain of the 2-oxyglutarate dehydrogenase complex from Azotobacter vinelandii

The three-dimensional solution structure of the lipoyl domain of the 2-oxoglutarate dehydrogenase complex from Azotobacter vinelandii has been determined from nuclear magnetic resonance data by using distance geometry and dynamical simulated annealing refinement. The structure determination is based on a total of 580 experimentally derived distance constraints and 65 dihedral angle constraints. The solution structure is represented by an ensemble of 25 structures with an average root-mean-square deviation between the individual structures of the ensemble and the mean coordinates of 0.71 Angstrom for backbone atoms and 1.08 Angstrom for all heavy atoms. The overall fold of the lipoyl domain is that of a beta-barrel-sandwich hybrid. It consists of two almost parallel four-stranded anti-parallel beta-sheets formed around a well-defined hydrophobic core, with a central position of the single tryptophan 21. The lipoylation site, lysine 42, is found in a beta-turn at the far end of one of the sheets, and is close in space to a solvent-exposed loop comprising residues 7 to 15. The lipoyl domain displays a remarkable internal symmetry that projects one beta-sheet onto the other beta-sheet after rotation of approximately 180 degrees about a 2-fold rotational symmetry axis. There is close structural similarity between the structure of this 2-oxoglutarate dehydrogenase complex lipoyl domain and the structures of the lipoyl domains of pyruvate dehydrogenase complexes from Bacillus Stearothermophilus and Escherichia coli, and conformational differences occur primarily in a solvent-exposed loop close in space to the lipoylation site. The lipoyl domain structure is discussed in relation to the process of molecular recognition of lipoyl domains by their parent 2-oxo acid dehydrogenase. (C) 1996 Academic Press Limited.