Substrate channelling in 2-oxo acid dehydrogenase multienzyme complexes

Abstract

Heteronuclear NMR spectroscopy and other experiments indicate that the true substrate of the E1 component of 2-oxo acid dehydrogenase complexes is not lipoic acid but the lipoyl domain of the E2 component. E1 can recognize the lipoyl-lysine residue as such, but reductive acylation ensues only if the domain to which the lipoyl group is attached is additionally recognized by virtue of a mosaic of contacts distributed chiefly over the half of the domain that contains the lipoyl-lysine residue. The lipoyl-lysine residue may not be freely swinging, as supposed hitherto, but may adopt a preferred orientation pointing towards a nearby loop on the surface of the lipoyl domain. This in turn may facilitate the insertion of the lipoyl group into the active site of E1, where reductive acylation is to occur. The results throw new light on the concept of substrate channelling and active-site coupling in these giant multifunctional catalytic machines.

Calcium-dependent activation of mitochondrial metabolism in mammalian cells

“…The enzymes contributing significantly to cellular flavoprotein fluorescence are localized in the mitochondrial matrix and have been assigned to lipoamide dehydrogenase and electron transfer flavoprotein (ETF) (27, 33–8). Lipoamide dehydrogenase is an integral component of the Ca 2+ -sensitive pyruvate and 2-oxoglutarate dehydrogenase complexes (39) and their flavin co-factors are in direct equilibrium with the mitochondrial NAD + /NADH pool. ETF is involved in the transfer of reducing equivalents to ubiquinone during β-oxidation of fatty acids (36).…”

Discovery of the catalytic function of a putative 2‐oxoacid dehydrogenase multienzyme complex in the thermophilic archaeon Thermoplasma acidophilum

“…1): a lipoyl moiety, covalently attached to a lysine residue in the lipoyl domain, serves as a swinging arm, connecting the active sites of each enzyme and channelling substrate through the complex [3]. Thus, E1 catalyses the thiamine pyrophosphate (TPP)-dependent oxidative decarboxylation of the 2-oxoacid and the transfer of the resulting acyl group to the lipoic acid of E2.…”

“…The complexes comprise multiple copies of three component enzymes: 2-oxoacid decarboxylase (E1), dihydrolipoyl acyltransferase (E2) and dihydrolipoamide dehydrogenase (E3) [1][2][3]. E2 forms the structural core of the complex, with multiple polypeptide chains associating into octahedral (24-mer) or icosahedral (60-mer) configurations, depending on the particular complex and the source organism [2,4].…”

Lipoic Acid-Dependent Oxidative Catabolism of α-Keto Acids in Mitochondria Provides Evidence for Branched-Chain Amino Acid Catabolism in Arabidopsis

“…Both of these enzyme complexes contain lipoic acid covalently bound to Lys residues of E2 enzymes. These lipoate moieties facilitate active site coupling between E1 and E3 enzymes by providing a means of acyl group movement for esterification to CoA and a mechanism of electron transfer to synthesize NADH (Reed, 1974;Perham et al, 2002). The further metabolism of these CoA esters has been investigated extensively through the reactions of the TCA cycle in mitochondria from many eukaryotes.…”

“…These complex structures use E1 (␣-keto acid dehydrogenase), E2 (acyltransferase), and E3 (lipoamide dehydrogenase) enzymes and five cofactors (TPP, CoA, lipoic acid, FAD ϩ , and NAD ϩ ) in their catalytic cycle (Reed, 1974;Mooney et al, 2002). Active-site coupling is used to catalyze decarboxylation of ␣-keto acids (E1 enzyme), esterification of aldehydes to CoA (E2 enzyme), and reduction of NAD ϩ to NADH (E3 enzyme; Reed, 1981;Perham et al, 2002). The most widely studied ␣-keto acid enzyme complexes are the pyruvate dehydrogenase complex (PDC) that regulates the entry of carbon into the tricarboxylic acid (TCA) cycle by the provision of acetyl-CoA and the ␣-ketoglutarate dehydrogenase complex (KGDC) that acts within the TCA cycle to synthesize succinylCoA.…”