L-threonine export:: Use of peptides to identify a new translocator from Corynebacterium glutamicum
L-threonine export:: Use of peptides to identify a new translocator from Corynebacterium glutamicum
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DOI：
10.1128/jb.183.18.5317-5324.2001
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发表时间：
2001-09-01
影响因子：
3.2
通讯作者：
Eggeling, L
中科院分区：
文献类型：
--
作者：
Simic, P;Sahm, H;Eggeling, L
细菌对肽的摄取及其水解为氨基酸的机制已经非常详细，而对肽衍生的氨基酸的命运知之甚少。我们发现，添加含有l -苏氨酸的二肽或三肽会导致谷氨酸杆状杆菌的生长减少，同时细胞内l -苏氨酸的高积累高达130 mM。通过转座子诱变和分离苏氨酸敏感性增加的突变体，鉴定出9个开放阅读框（orf），几乎所有的orf编码功能未知的假设蛋白。三个orf编码膜蛋白。它们在野生型背景下的个体功能特征导致了三种re的鉴定。当三re过表达时，生长不再对苏氨酸肽的存在敏感，l -苏氨酸的输出速率为3.8 nmol min(-1) mg干重（-1），而三re失活突变体的输出速率降低到1.1 nmol min(-1) mg干重（-1）。除了l -苏氨酸，l -丝氨酸也是出口商的底物。输出物显示出九个预测的跨膜螺旋，带有长电荷的C和N端，并在N端存在一个两亲螺旋。所有这些数据表明，由3 - re编码的载体用于输出l -苏氨酸等小分子，并且该载体是一个新的转运体家族的原型。three的同源物存在于结核分枝杆菌和冷色链霉菌中。
Bacterial mechanisms for the uptake of peptides and their hydrolysis to amino acids are known in great detail, whereas much less is known about the fates of the peptide-derived amino acids. We show that the addition Of L-threonine-containing di- or tripeptides results in reduction of the growth of Corynebacterium glutamicum, with concomitant high intracellular accumulation Of L-threonine to up to 130 mM. Using transposon mutagenesis and isolation of mutants with increased Thr peptide sensitivity, nine open reading frames (ORFs) were identified, almost all encoding hypothetical proteins of unknown function. Three ORFs encode membrane proteins. Their individual functional characterizations in the wild-type background led to the identification of thrE. Upon thrE overexpression, growth is no longer sensitive to the presence of the Thr peptide, and L-threonine is exported at a rate of 3.8 nmol min(-1) mg of dry weight(-1), whereas the rate of export of a thrE inactivation mutant is reduced to 1.1 nmol min(-1) mg of dry weight(-1). In addition to L-threonine, L-serine is also a substrate for the exporter. The exporter exhibits nine predicted transmembrane-spanning helices with long charged C and N termini and with an amphipathic helix present within the N terminus. All these data suggest that the carrier encoded by thrE serves to export small molecules such as L-threonine and that the carrier is a prototype of a new translocator family. Homologues of ThrE are present in Mycobacterium tuberculosis and Streptomyces coelicolor.