CONSTRUCTION AND PROPERTIES OF PYRUVATE-DEHYDROGENASE COMPLEXES WITH UP TO 9 LIPOYL DOMAINS PER LIPOATE ACETYLTRANSFERASE CHAIN

The lipoate acetyltransferase (E2p) subunits of the pyruvate dehydrogenase (PDH) complex of Escherichia coli have three tandemly repeated lipoyl domains, although net deletions of one or two has no apparent effect on the activity of the purified complexes. Plasmids containing IPTG-inducible aceEF-lpd operons, which encode PDH complexes bearing from one to nine lipoyl domains per E2p chain (24-216 per complex), were constructed. They were all capable of restoring the nutritional lesion of a strain lacking PDH complex and they all expressed active sedimentable multienzyme complexes having a relatively normal range of subunit stoichiometries. The extra domains are presumed to protrude from the E2p core (24-mer) without significantly affecting the assembly of the E1p and E3 subunits on the respective edges and faces of the cubic core. However, the catalytic activities of the overproduced complexes containing four to nine lipoyl domains per E2p chain were lower than those with fewer lipoyl domains. This could be due to under-lipoylation of the domains participating in catalysis and interference from unlipoylated domains.