| Type: | Family | Name: | 2-oxoacid:acceptor oxidoreductase, alpha subunit |
| Description: | This entry represents the alpha subunit of 2-oxoacid:acceptor oxidoreductases, which catalyse CoA-dependent oxidative decarboxylation of 2-oxoacids. Proteins in this family contain a thiamine diphosphate (TPP) binding domain typical of flavodoxin/ferredoxin oxidoreductases (), and an N-terminal domain similar to the gamma subunit of the same group of oxidoreductases (). The genes encoding the proteins are always found in association with a neighbouring gene for a beta subunit () which also occurs in a four-subunit (alpha/beta/gamma/ferredoxin) version of the system. This pair of genes is not consistently observed in proximity to any electron acceptor genes, but is found next to putative ferredoxins or ferredoxin-domain proteins in Aromatoleum aromaticum EbN1, Bradyrhizobium japonicum USDA 110, Frankia sp CcI3, Rhodoferax ferrireducens T118, Rhodopseudomonas palustris BisB5, Os, Sphingomonas wittichii RW1and Streptomyces clavuligerus. Other potential acceptors are also sporadically observed in close proximity including ferritin-like proteins, reberythrin, peroxiredoxin and a variety of other flavin and iron-sulfur cluster-containing proteins.The phylogenetic distribution of this family encompasses archaea, a number of deeply-branching bacterial clades and only a small number of firmicutes and proteobacteria. The enzyme from Sulfolobus has been characterised with respect to its substrate specificity [] which is described as wide, encompassing various 2-oxoacids such as 2-oxoglutarate, 2-oxobutyrate and pyruvate. Halobacterium salinarum (and most halophilic archaea) contains two 2-oxoacid:ferredoxin oxidoreductases. One (Kor) functions as an oxoglutarate-ferredoxin oxidoreductase [], whereas the other (Por) has been characterised as a pyruvate-ferredoxin oxidoreductase [, , ].The enzyme from Hydrogenobacter thermophilushas been shown to have a high specificity towards 2-oxoglutarate [, ] and is one of the key enzymes in the reverse TCA cycle in this organism. Furthermore, considering its binding of coenzyme A (CoA), it can be reasonably inferred that the product of the reaction is succinyl-CoA. The genes for this enzyme in Prevotella intermedia 17, Persephonella marina EX-H1and Picrophilus torridus DSM 9790are in close proximity to a variety of TCA cycle genes. Persephonella marina and P. torridus [] are believed to encode complete TCA cycles, and none of these contains the lipoate-based 2-oxoglutarate dehydrogenase (E1/E2/E3) system. That system is presumed to be replaced by this one. In fact, the lipoate system is absent in most organisms possessing a member of this family, providing additional circumstantial evidence that many of these enzymes are capable of acting as 2-oxoglutarate dehydrogenases and supporting flux through TCA cycles in either the forward or reverse directions. | Short Name: | 2-oxoacid/accept_OxRdtase_asu |
