Regulation of the ald Gene Encoding Alanine Dehydrogenase by AldR in Mycobacterium smegmatis
Regulation of the ald Gene Encoding Alanine Dehydrogenase by AldR in Mycobacterium smegmatis
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DOI：
10.1128/jb.00482-13
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发表时间：
2013-08-01
影响因子：
3.2
通讯作者：
Oha, Jeong-Il
中科院分区：
文献类型：
--
作者：
Jeong, Ji-A;Baek, Eun-Young;Oha, Jeong-Il
在耻垢分枝杆菌中，在编码L-丙氨酸脱氢酶的ald基因上游95 bp处鉴定出调节基因aldR。AldR蛋白与Lrp/AsnC家族的调节蛋白序列相似。使用一个aldR缺失突变体，我们证明，AldR作为激活剂和抑制剂的ALD基因表达的调节，这取决于L-丙氨酸的存在或不存在。纯化的AldR蛋白在不存在L-丙氨酸的情况下作为同二聚体存在，而在存在L-丙氨酸的情况下其采用同六聚体的四级结构。AldR对ALD控制区的结合亲和力被证明是由L-丙氨酸显着增加。在ald基因上游发现了两个AldR结合位点（O 1和O2），其共有序列为GA-N-2-ATC-N-2-TC，一个推测的AldR结合位点为GA-N-2-GTT-N-2-TC。丙氨酸和半胱氨酸被证明是直接参与诱导ald表达的效应分子。L-丙氨酸在M.在缺氧条件下生长的乳腺癌细胞中，ALD表达的缺氧诱导似乎是由AldR介导的，其感测丙氨酸的细胞内水平。
The regulatory gene aldR was identified 95 bp upstream of the ald gene encoding L-alanine dehydrogenase in Mycobacterium smegmatis. The AldR protein shows sequence similarity to the regulatory proteins of the Lrp/AsnC family. Using an aldR deletion mutant, we demonstrated that AldR serves as both activator and repressor for the regulation of ald gene expression, depending on the presence or absence of L-alanine. The purified AldR protein exists as a homodimer in the absence of L-alanine, while it adopts the quaternary structure of a homohexamer in the presence of L-alanine. The binding affinity of AldR for the ald control region was shown to be increased significantly by L-alanine. Two AldR binding sites (O1 and O2) with the consensus sequence GA-N-2-ATC-N-2-TC and one putative AldR binding site with the sequence GA-N-2-GTT-N-2-TC were identified upstream of the ald gene. Alanine and cysteine were demonstrated to be the effector molecules directly involved in the induction of ald expression. The cellular level of L-alanine was shown to be increased in M. smegmatis cells grown under hypoxic conditions, and the hypoxic induction of ald expression appears to be mediated by AldR, which senses the intracellular level of alanine.