Abstract
A 79-amino-acid polypeptide, corresponding to the lipoyl domain of the succinyltransferase component of the 2-oxoglutarate dehydrogenase multienzyme complex from Azotobacter vinelandii, has been sub-cloned and produced in Escherichia coli. Complete sequential 1H and 15N resonance 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 connectivities and 3JHN alpha values. The lipoyl-lysine residue is found in a type-I turn connecting two beta-strands. The secondary structure of the lipoyl domain very much resembles the secondary solution structure of the N-terminal lipoyl domain of the A. vinelandii pyruvate dehydrogenase complex, despite the sequence identity of 25%. A detailed comparison of the NMR-derived parameters of both lipoyl domains, i.e. chemical shifts, NH-exchange rates, NOEs, and 3JHN alpha values suggests a high structural similarity in solution between the two lipoyl domains. Preliminary tertiary-structure calculations confirm that these lipoyl domains have very similar overall folds. The observed specificity of the 2-oxo acid dehydrogenase components of both complexes for these lipoyl domains is discussed in this respect.
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