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PubMed1984

Repeating functional domains in the pyruvate dehydrogenase multienzyme complex of Escherichia coli.

Each polypeptide chain in the lipoate acetyltransferase (E2) core of the pyruvate dehydrogenase complex from Escherichia coli contains three repeating sequences in the N-terminal half of the molecule. The repeats are highly homologous in primary structure and each includes a lysine residue that is a potential site for lipoylation. We have shown that all three sites are lipoylated, at least in part, and that the three lipoylated segments of the E2 chain can be isolated as distinct functional domains after limited proteolysis. Each domain becomes partly acetylated in the intact complex in the presence of substrate. In the primary structure, the domains are separated by regions of polypeptide chain oddly rich in alanine and proline residues. These regions are probably the conformationally mobile segments observed in the 1H-n.m.r. spectrum of the complex and which are removed by tryptic cleavage at Lys-316. The C-terminal half of the molecule contains the acetyltransferase active site and the binding sites for E1, E3 and other E2 subunits. The pyruvate dehydrogenase complex of E. coli, which has a heterogeneous quaternary structure, is thus far unique among the 2-oxo acid dehydrogenase complexes in possessing more than one lipoyl domain per E2 chain, but this may be a general feature of the enzyme from Gram-negative organisms.

Amino Acid Sequence↗
PubMed1983

Multienzyme complexes of fatty acid oxidation from Escherichia coli K12 and from a mutant with a defective L-3-hydroxyacyl coenzyme A dehydrogenase.

An Escherichia coli mutant (fadB64), with a defective L-3-hydroxyacyl-CoA dehydrogenase (EC 1.1.1.35) which is unable to grow on long-chain fatty acids as the sole carbon source, was shown to possess a fatty acid oxidation complex that contains five beta-oxidation enzymes, including L-3-hydroxyacyl-CoA dehydrogenase. A comparative study of the complexes from the mutant, from its parental strain and from wild-type E. coli B demonstrated the immunological and gross structural identity of all three fatty acid oxidation complexes. A kinetic evaluation of the complexes led to the suggestion that the mutation may have affected the active site of L-3-hydroxyacyl-CoA dehydrogenase so that it is inactive with acetoacetyl-CoA as a substrate, but exhibits an increasing percentage of the parental dehydrogenase activity with increasing chain length of the substrate.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1971

The effect of 2H2O on the quaternary structure of the fatty acid synthetase multienzyme complex.

The effect of 2H2O on the cold-induced dissociation and cold-induced inactivation of fatty acid synthetase from lactating mammary gland has been studied. The rate constants for these reactions were almost identical and were lowered in media containing 2H2O. The results have been interpreted to indicate that inactivation of the enzyme in the cold is a direct result of dissociation into subunits and that maintenance of the native structure of the enzyme is limited by the strength of hydrophobic bonds.

Animals↗
PubMed1989

Antibodies against an inter-domain segment of polypeptide chain inhibit active-site coupling in the pyruvate dehydrogenase multienzyme complex.

A synthetic peptide, AAPAAAPAKQEAAAPAPAAKAEAPAAAPAAKA, proved to be an efficient and specific immunogen in rabbits. The amino acid sequence of the peptide is identical to that of the inter-domain region (PEP3) linking the innermost of the three lipoyl domains to the dihydrolipoamide dehydrogenase-binding domain in the dihydrolipoamide acetyltransferase chain of the pyruvate dehydrogenase complex of Escherichia coli. Fab fragments from anti-PEP3 antibodies selectively inhibited active-site coupling in the complex without affecting the individual activities of the three component enzymes, highlighting the role of the inter-domain regions as flexible linkers in catalysis.

Antibodies↗