Biomedical subjects

A F Hengeveld

Publications and source records attributed to A F Hengeveld.

4 recordsLinked to original sources

PubMed2002

Structural basis of the dysfunctioning of human 2-oxo acid dehydrogenase complexes.

2-oxo acid dehydrogenase complexes are a ubiquitous family of multienzyme systems that catalyse the oxidative decarboxylation of various 2-oxo acid substrates. They play a key role in the primary energy metabolism: in glycolysis (pyruvate dehydrogenase complex), the citric acid cycle (2-oxoglutarate dehydrogenase complex) and in amino acid catabolism (branched-chain 2-oxo acid dehydrogenase complex). Malfunctioning of any of these complexes leads to a broad variety of clinical manifestations. Deficiency of the pyruvate dehydrogenase complex predominantly leads to lactic acidosis combined with impairment of neurological function and/or delayed growth and development. Maple urine disease is an inborn metabolic error caused by dysfunction of the branched-chain 2-oxo acid dehydrogenase complex. An association between both Alzheimer disease and Parkinson s disease and the 2-oxoglutarate dehydrogenase gene has been reported. Currently a wealth of both genetic and structural information is available. Three-dimensional structures of three components of the complex are presently available: of the pyruvate dehydrogenase component (E1), of the dihydrolipoyl acyltransferase component (E2) and of the lipoamide dehydrogenase component (E3). Moreover, detailed information on the reaction mechanism, regulation and the interactions between the different components of the complex is now at hand. Although only one of the structures is of human origin (E1b), model building by homology modelling allows us to investigate the causes of dysfunction. In this review we have combined this knowledge to gain more insight into the structural basis of the dysfunctioning of the 2-oxo acid dehydrogenase complexes.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗

PubMed1999

Pyruvate dehydrogenase from Azotobacter vinelandii. Properties of the N-terminally truncated enzyme.

The pyruvate dehydrogenase multienzyme complex (PDHC) catalyses the oxidative decarboxylation of pyruvate and the subsequent acetylation of coenzyme A to acetyl-CoA. Previously, limited proteolysis experiments indicated that the N-terminal region of the homodimeric pyruvate dehydrogenase (E1p) from Azotobacter vinelandii could be involved in the binding of E1p to the core protein (E2p) [Hengeveld, A. F., Westphal, A. H. & de Kok, A. (1997) Eur J. Biochem. 250, 260-268]. To further investigate this hypothesis N-terminal deletion mutants of the E1p component of Azotobacter vinelandii pyruvate dehydrogenase complex were constructed and characterized. Up to nine N-terminal amino acids could be removed from E1p without effecting the properties of the enzyme. Truncation of up to 48 amino acids did not effect the expression or folding abilities of the enzyme, but the truncated enzymes could no longer interact with E2p. The 48 amino acid deletion mutant (E1pdelta48) is catalytically fully functional: it has a Vmax value identical to that of wild-type E1p, it can reductively acetylate the lipoamide group attached to the lipoyl domain of the core enzyme (E2p) and it forms a dimeric molecule. In contrast, the S0.5 for pyruvate is decreased. A heterodimer was constructed containing one subunit of wild-type E1p and one subunit of E1pdelta48. From the observation that the heterodimer was not able to bind to E2p, it is concluded that both N-terminal domains are needed for the binding of E1p to E2p. The interactions are thought to be mainly of an electrostatic nature involving negatively charged residues on the N-terminal domains of E1p and previously identified positively charged residues on the binding and catalytic domain of E2p.

Amino Acid Sequence↗

PubMed1998

The pyruvate dehydrogenase multi-enzyme complex from Gram-negative bacteria.

Pyruvate dehydrogenase multi-enzyme complexes from Gram-negative bacteria consists of three enzymes, pyruvate dehydrogenase/decarboxylase (E1p), dihydrolipoyl acetyltransferase (E2p) and dihydrolipoyl dehydrogenase (E3). The acetyltransferase harbors all properties required for multi-enzyme catalysis: it forms a large core of 24 subunits, it contains multiple binding sites for the E1p and E3 components, the acetyltransferase catalytic site and mobile substrate carrying lipoyl domains that visit the active sites. Today, the Azotobacter vinelandii complex is the best understood oxo acid dehydrogenase complex with respect to structural details. A description of multi-enzyme catalysis starts with the structural and catalytic properties of the individual components of the complex. Integration of the individual properties is obtained by a description of how the many copies of the individual enzymes are arranged in the complex and how the lipoyl domains couple the activities of the respective active sites by way of flexible linkers. These latter aspects are the most difficult to study and future research need to be aimed at these properties.

Acetyltransferases↗

PubMed1997

Expression and characterisation of the homodimeric E1 component of the Azotobacter vinelandii pyruvate dehydrogenase complex.

We have cloned and sequenced the gene encoding the homodimeric pyruvate dehydrogenase component (E1p) of the pyruvate dehydrogenase complex from Azotobacter vinelandii and expressed and purified the E1p component in Escherichia coli. Cloned E1p can be used to fully reconstitute complex activity. The enzyme was stable in high ionic strength buffers, but was irreversibly inactivated when incubated at high pH, which presumably was caused by its inability to redimerize correctly. This explains the previously found low stability of the wild-type E1p component after resolution from the complex at high pH. Cloned E1p showed a kinetic behaviour exactly like the wild-type complex-bound enzyme with respect to its substrate (pyruvate), its allosteric properties, and its effectors. These experiments show that acetyl coenzyme A acts as a feedback inhibitor by binding to the E1p component. Limited proteolysis experiments showed that the N-terminal region of E1p was easily removed. The resulting protein fragment was still active with artificial electron acceptors but had lost its ability to bind to the core component (E2p) and thus reconstitute complex activity. E1p was protected against proteolysis by E2p. The allosteric effector pyruvate changed E1p into a conformation that is more resistant to proteolysis.

Amino Acid Sequence↗