Chain folding in the dihydrolipoyl acyltransferase components of the 2-oxo-acid dehydrogenase complexes from Escherichia coli. Identification of a segment involved in binding the E3 subunit.

The state of assembly of the pyruvate and 2-oxoglutarate dehydrogenase multienzyme complexes was examined after the dihydrolipoyl acyltransferase (E2) component of each enzyme system had been subjected to varying degrees of limited proteolysis. Dissociation of the dihydrolipoyl dehydrogenase (E3) component accompanied specifically the excision of a homologous segment of each E2 chain that connects the N-terminal lipoyl domain(s) with a C-terminal catalytic domain. The latter remains aggregated as a 24-mer and retains its capacity to bind the 2-oxo-acid decarboxylase (E1) component. The relevant segment of the E2o chain from the 2-oxoglutarate dehydrogenase complex was isolated and shown to be a folded protein which still binds to E3.