SEQUENTIAL H-1 AND N-15 NUCLEAR-MAGNETIC-RESONANCE ASSIGNMENTS AND SECONDARY STRUCTURE OF THE LIPOYL DOMAIN OF THE 2-OXOGLUTARATE DEHYDROGENASE COMPLEX FROM AZOTOBACTER-VINELANDII - EVIDENCE FOR HIGH STRUCTURAL SIMILARITY WITH THE LIPOYL DOMAIN OF THE PYRUVATE-DEHYDROGENASE COMPLEX

A 79-amino-acid polypeptide, corresponding to the lipoyl domain of the succinyltransferase component of the 2-oxoglutarate dehydrogenase mul tienzyme complex from Azotobacter vinelandii, has been sub-cloned and produced in Escherichia coli. Complete sequential H-1 and N-15 resonan ce assignments for the lipoyl domain have been obtained by using homo- and hetero-nuclear NMR spectroscopy. Two antiparallel beta-sheets of four strands each were identified from characteristic NOE connectiviti es and (3)J(HN alpha) values. The lipoyl-lysine residue is found in a type-I turn connecting two beta-strands. The secondary structure of th e lipoyl domain very much resembles the secondary solution structure o f the N-terminal lipoyl domain of the A. vinelandii pyruvate dehydroge nase complex, despite the sequence identity of 25%. A detailed compari son of the NMR-derived parameters of both lipoyl domains, i.e. chemica l shifts, NH-exchange rates, NOEs, and (3)J(HN alpha) values suggests a high structural similarity in solution between the two lipoyl domain s. Preliminary tertiary-structure calculations confirm that these lipo yl domains have very similar overall folds. The observed specificity o f the 2-oxo acid dehydrogenase components of both complexes for these lipoyl domains is discussed in this respect.