Aerobic Benzoyl-Coenzyme A (CoA) Catabolic Pathway in Azoarcus evansii : Conversion of Ring Cleavage Product by 3,4-Dehydroadipyl-CoA Semialdehyde Dehydrogenase

Abstract

Benzoate, a strategic intermediate in aerobic aromatic metabolism, is metabolized in various bacteria via an unorthodox pathway. The intermediates of this pathway are coenzyme A (CoA) thioesters throughout, and ring cleavage is nonoxygenolytic. The fate of the ring cleavage product 3,4-dehydroadipyl-CoA semialdehyde was studied in the ␤-proteobacterium Azoarcus evansii. Cell extracts contained a benzoate-induced, NADP ؉ -specific aldehyde dehydrogenase, which oxidized this intermediate. A postulated putative long-chain aldehyde dehydrogenase gene, which might encode this new enzyme, is located on a cluster of genes encoding enzymes and a transport system required for aerobic benzoate oxidation. The gene was expressed in Escherichia coli, and the maltose-binding protein-tagged enzyme was purified and studied. It is a homodimer composed of 54 kDa (without tag) subunits and was confirmed to be the desired 3,4-dehydroadipyl-CoA semialdehyde dehydrogenase. The reaction product was identified by nuclear magnetic resonance spectroscopy as the corresponding acid 3,4-dehydroadipyl-CoA. Hence, the intermediates of aerobic benzoyl-CoA catabolic pathway recognized so far are benzoyl-CoA; 2,3-dihydro-2,3-dihydroxybenzoyl-CoA; 3,4-dehydroadipyl-CoA semialdehyde plus formate; and 3,4-dehydroadipyl-CoA. The further metabolism is thought to lead to 3-oxoadipyl-CoA, the intermediate at which the conventional and the unorthodox pathways merge.

Anaerobic Catabolism of Aromatic Compounds: a Genetic and Genomic View

“…The aerobic degradation of benzoate in some facultative anaerobes also starts with the activation of this aromatic acid via a benzoate-CoA ligase (box pathway) that shows similarity to the anaerobic benzoate-CoA ligases (124,125,238). Interestingly, these types of aerobic hybrid pathways that are initiated through the formation of CoA thioesters (although they still make use of oxygen to introduce hydroxyl groups into the aromatic ring) have been considered to be an adaptation of some denitrifying facultative aerobes to fluctuating oxic/anoxic conditions, since both oxic and anoxic types of catabolism share the same initial aryl-CoA intermediates as substrates (116).…”

Coenzyme A-dependent Aerobic Metabolism of Benzoate via Epoxide Formation

“…Box His C Strep was purified similar to BoxB Strep ; the column was washed with 60 ml of buffer A and 180 ml of buffer A containing 100 mM KCl. BoxD Mal was purified as described (12).…”

“…BoxD, a homodimer composed of 54-kDa subunits, is a NADP ϩ -specific aldehyde dehydrogenase that oxidizes the product of BoxC, 3,4-dehydroadipyl-CoA semialdehyde, to the corresponding acid, 3,4-dehydroadipyl-CoA (12). The further metabolism probably requires a kind of ␤-oxidation leading to ␤-ketoadipyl-CoA, the last intermediate at which the conventional ␤-ketoadipate pathway and the unorthodox new pathway merge (4,7).…”

Bacterial Degradation of Benzoate

“…The 3,4-dehydroadipyl-CoA semialdehyde formed becomes converted to succinyl-CoA and acetyl-CoA by a ␤-oxidation-like metabolism (box lower pathway) (Fig. 1A) (8,(13)(14)(15)(16)(17)(18)(19)(20)(21)(22).…”