3-DIMENSIONAL STRUCTURE OF A LIPOYL DOMAIN FROM THE DIHYDROLIPOYL ACETYLTRANSFERASE COMPONENT OF THE PYRUVATE-DEHYDROGENASE MULTIENZYME COMPLEX OF ESCHERICHIA-COLI

The structure of a lipoyl domain from the pyruvate dehydrogenase multi enzyme complex of Escherichia coli has been determined by means of nuc lear magnetic resonance spectroscopy A total of 549 nuclear Overhauser effect distance restraints, 52 phi torsion angle restraints and 16 sl owly exchanging amide protons were employed as input for the structure calculations. These were performed using a combined distance geometry -simulated annealing strategy The domain is a hybrid between the N and C-terminal halves of the first and third lipoyl domains, respectively of the dihydrolipoyl acetyltransferase component of the E. coli multi enzyme complex, representing residues 1 to 33 and 238 to 289 (wild-typ e numbering). The lipoyl-lysine residue was also replaced by glutamine . Nonetheless, its structure, two four-stranded beta-sheets forming a flattened beta-barrel, closely resembles that of the lipoyl domain fro m the pyruvate dehydrogenase multienzyme complex from Bacillus stearot hermophilus determined previously: As before, the lipoylation site is physically exposed in a tight turn in one of the beta-sheets, and the N and C-terminal residues are close together at the other end of the m olecule in adjacent strands of the other beta-sheet. Another prominent ly conserved feature of the structure is the 2-fold axis of quasi-symm etry relating the N and C-terminal halves of the domain. Consistent wi th the high level of sequence similarity between lipoyl domains of 2-o xo acid dehydrogenase multienzyme complexes from many different source s, these results confirm that all lipoyl domains are likely to have cl osely related structures.