Isolation and characterization of a bile acid inducible 7alpha-dehydroxylating operon in Clostridium hylemonae TN271.
Isolation and characterization of a bile acid inducible 7alpha-dehydroxylating operon in Clostridium hylemonae TN271.
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DOI：
10.1016/j.anaerobe.2009.05.004
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发表时间：
2010-04
期刊：
影响因子：
2.3
通讯作者：
Hylemon PB
中科院分区：
文献类型：
--
作者：
Ridlon JM;Kang DJ;Hylemon PB
初级胆汁酸由肝脏中的胆固醇合成，与甘氨酸或牛磺酸结合并分泌到胆汁中。胆盐每天经肠肝循环数次。在这个过程中，它们被肠道细菌生物转化为各种代谢物。主要的生物转化是胆酸和鹅去氧胆酸的7α-去羟基化反应，分别生成去氧胆酸和石胆酸。7α-去羟基化是一个多步骤的途径。在两种“高”活性梭菌菌株中已鉴定出编码该途径酶的基因。本文报道了一种低活性7α-去羟基菌株——水合梭菌（Clostridium hylemonae）中胆汁酸诱导（bai）操纵子的分离和特性。baiBCDEFGHI操纵子的基因组织和序列在水门c菌和“高”活性菌株之间高度保守。令人惊讶的是，在C. hylemonae的bai操纵子中缺少baiA基因。采用聚合酶链反应和简并寡核苷酸引物分离baiA基因。确定了大bai操纵子的mRNA起始位点，显示其距离第一个基因的起始密码子仅11bp。此外，还发现异胆酸（5α）诱导白操纵子，刺激异胆酸的形成。最后发现，在生长培养基中添加睾酮可显著提高香茅和水茅中胆酸的7α-去羟基化。我们假设睾酮可能是参与胆汁酸7α-去羟基化途径还原臂的基因的无端诱导剂。
Primary bile acids are synthesized from cholesterol in the liver, conjugated to either glycine or taurine and secreted into bile. Bile salts undergo enterohepatic circulation several times each day. During this process, they are biotransformed into a variety of metabolites by gut bacteria. The major biotransformation is the 7α-dehydroxylation of cholic acid and chenodeoxycholic acid yielding deoxycholic acid and lithocholic acid, respectively. 7α-Dehydroxylation is a multi-step pathway. The genes encoding enzymes in this pathway have been identified in two species of “high” activity strains of clostridia. Here, we report the isolation and characterization of a bile acid inducible (bai) operon in Clostridium hylemonae, a “low” activity 7α-dehydroxylating strain. The gene organization and sequence of the baiBCDEFGHI operon was highly conserved between C. hylemonae and “high” activity strains. Surprisingly, the baiA gene was missing from the bai operon of C. hylemonae. The baiA gene was isolated using PCR and degenerate oligonucleotide primers. The mRNA start site for the large bai operon was determined and shown to be only 11 bp from the initiation codon of the first gene. It was also discovered that allocholic acid (5α) induced the bai operon and stimulated the formation of allodeoxycholic acid. Finally, it was discovered that the addition of testosterone to the growth medium markedly increased 7α-dehydroxylation of cholic acid in C. scindens and C. hylemonae. We hypothesize that testosterone may be a gratuitous inducer of genes involved in the reductive arm of the bile acid 7α-dehydroxylation pathway.
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影响因子：
3.3
作者：
Pai, R;Tarnawski, AS;Tran, T
通讯作者：
Tran, T
影响因子：
3.2
作者：
MALLONEE, DH;WHITE, WB;HYLEMON, PB
通讯作者：
HYLEMON, PB
DOI：
10.1016/0022-4731(76)90187-4
发表时间：
1976-01-01
影响因子：
4.1
作者：
BOKKENHEUSER, VD;WINTER, J;KELLY, WG
通讯作者：
KELLY, WG
DOI：
10.1016/0005-2760(79)90066-3
发表时间：
1979-01-01
期刊：
BIOCHIMICA ET BIOPHYSICA ACTA
影响因子：
--
作者：
GLASS, TL;WHEELER, LA;FINEGOLD, SM
通讯作者：
FINEGOLD, SM
影响因子：
3.2
作者：
GOPALSRIVASTAVA, R;MALLONEE, DH;HYLEMON, PB
通讯作者：
HYLEMON, PB