Evidence for a multigene family involved in bile acid 7-dehydroxylation in Eubacterium sp. strain VPI 12708

Abstract

Eubacterium sp. strain VPI 12708 is a human intestinal isolate which has an inducible bile acid 7-dehydroxylation activity. At least two cholic acid-induced polypeptides, with molecular masses of 27,000 and 45,000 daltons, respectively, coelute with bile acid 7-dehydroxylation activity. The 45,000-dalton polypeptide appears to be encoded by a cholic acid-induced mRNA species of greater than 6 kilobases, which suggests that the gene coding for this polypeptide is part of a larger operon. A gene has been cloned which flanks the gene encoding the 45,000-dalton polypeptide, in the upstream (5') direction. This gene appears to encode a second 27,000-dalton polypeptide. The gene bears striking homology at both the nucleotide (80%) and deduced amino acid sequence (89%) levels with the gene which encodes the 27,000-dalton polypeptide that has been shown previously to be involved in the bile acid 7-dehydroxylation reaction sequence. The implications of this homology and the possible function(s) of the two homologous genes in bile acid 7-dehydroxylation are discussed. Evidence is presented which suggests that the two homologous genes involved in bile acid 7-dehydroxylation may be part of a larger multigene family in Eubacterium sp. strain VPI 12708.

Prokaryotic 20β‐hydroxysteroid dehydrogenase is an enzyme of the ‘short‐chain, non‐metalloenzyme’ alcohol dehydrogenase type

“…Consequently, it may be concluded that the 'short-chain dehydrogenase family' includes not only insect alcohol dehydrogenase [2] and prokaryotic dehydrogenases of sugar metabolism [4], but also prokaryotic steroid dehydrogenases. This is compatible with the further inclusion of two other proteins involved in prokaryotic dehydroxylation [5,6] and suggests that they are also hydroxysteroid dehydrogenases. The results enlarge the short-chain alcohol dehydrogenase family and establish it to include many different enzyme specificities.…”

“…The classical liver and yeast alcohol dehydrogenases belong to the latter family, the insect enzyme to the former, and was long ago found to be different [3]. Divergent members of the 'short-chain dehydrogenase type' have been characterized and additional sugar, steroid and other dehydrogenases were added to the family [2,[4][5][6][7], as well as species variants for the Drosophila alcohol dehydrogenase [8]. The enzymes initially characterized were non-mammalian, but recently mammalian proteins have also been found to belong to this group, thus linking a human prostaglandin [9] and a human steroid dehydrogenase [10,11] to the prokaryotic/insect short-chain dehydrogenase type.…”

Bile salt biotransformations by human intestinal bacteria

“…Purification and N-terminal sequencing of these bai polypeptides facilitated the cloning of bai genes through the design of degenerate probes (121)(122)(123). Northern blot analysis indicated the presence of a large CA-inducible (>10 kb) mRNA transcript and a smaller transcript (<1.5 kb) in C. scindens (121,124). These studies led to the discovery of a bai regulon encoding at least 10 open reading frames (Fig.…”

“…Oxidation of the 3-hydroxy group inhibits 7a-hydroxy group dehydrogenation, favoring 7-dehydroxylation over constitutively expressed 7a-HSDHs in C. scindens (58,80). The baiA gene products encode 27 kDa polypeptides that have significant similarity with the short-chain alcohol/ polyol dehydrogenase gene family (58,124). Amino acid multiple sequence alignment and comparison between baiA gene products and other members of the short-chain alcohol dehydrogenase family revealed a possible NAD(P) binding site and catalytic active site (58).…”

The bile acid-inducible baiB gene from Eubacterium sp. strain VPI 12708 encodes a bile acid-coenzyme A ligase

“…Three of these inducible polypeptides have been purified, and the genes encoding them have been cloned and sequenced (5,6,20,38). One of the purified polypeptides, a 27,000-Mr species, is encoded by three separate genes (baiAl, baiA42, and baiA3) (5,6,13,39). One of these three gene copies (baiA2) resides on a large bile acid-inducible operon (20).…”