THE PRIMARY STRUCTURE OF BRANCHED-CHAIN ALPHA-OXO ACID DEHYDROGENASE FROM BACILLUS-SUBTILIS AND ITS SIMILARITY TO OTHER ALPHA-OXO ACID DEHYDROGENASES

The bfmB mutant of Bacillus subtilis requires branched short-chain carboxylic acids for growth because the organism is known to be defective in branched-chain a-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 E1alpha, E1beta and E2 components of pyruvate, 2-oxoglutarate and branched-chain alpha-oxo acid dehydrogenases from different sources. The thiamin diphosphate binding, putative subunit interaction and phosphorylation sites of the E1alpha of four reported branched-chain alpha-oxo acid dehydrogenases from different sources are very similar to those of the first open reading frame (E1alpha) of bfmB. A similar result is also obtained with the lipoyl-binding site (lysine) and its domain of the E2 component of alpha-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 alpha-oxo acid dehydrogenase, which is composed of E1alpha, E1beta and E2 genes. This organization is identical to that of the 2-oxoglutarate dehydrogenase in B. subtilis.