The primary structure of branched-chain α-oxo acid dehydrogenase from Bacillus subtilis and its similarity to other α-oxo acid dehydrogenases

The bfmB muant of Bacillus subtilis requires branched short-chain carboxylic acids for growth because the organism is known to be defective in branced-chain α-oxo acid dehydrogenase. The DNA in the region of bfmB has now been cloned and sequenced, and the gene has been analyzed. The results show that there are three open reading frames in the area, each of which is preceded by a putative ribosome binding site, and the last of which is followed by a putative transcription termination site with inverted repeats. The amino acid sequences deduced by analysis of the reading frames are highly similar (with 32–49% identity) to the E1α, E1β and E2 components of pyruvate, 2-oxoglutarate and branched-chain α-oxo acid dehydrogenases from different sources. The thiamin diphosphate binding, putative subunit interaction and phosphorylation sites of the E1α of four reported branched-chain α-oxo acid dehydrogenases from different sources are very similar to those of the first open reading frame (E1α) of bfmB. A similar result is also obtained with the lipoylbinding site (lysine) and its domain of the E2 component of α-oxo acid dehydrogenases from different sources. The present data, along with the reported biochemical data, lead to the conclusion that bfmB encodes a branched-chain α-oxo acid dehydrogenase, which is composed of E1α, E1β and E2 genes. This organization is identical to that of the 2-oxoglutarate dehydrogenase in B. subtilis.