Sequential 1H and 15N Nuclear Magnetic Resonance Assignments and Secondary Structure of the Lipoyl Domain of the 2‐Oxoglutarate Dehydrogenase Complex from Azotobacter Vinelandii

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 anti‐parallel β‐sheets of four strands each were identified from characteristic NOE connectivities and 3JHNα values. The lipoyl‐lysine residue is found in a type‐I turn connecting two β‐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 3JHNα 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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