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首页> 外文期刊>Journal of bacteriology >Genetic and Biochemical Characterization of a High-Affinity Betaine Uptake System (BusA) in Lactococcus lactisReveals a New Functional Organization within Bacterial ABC Transporters
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Genetic and Biochemical Characterization of a High-Affinity Betaine Uptake System (BusA) in Lactococcus lactisReveals a New Functional Organization within Bacterial ABC Transporters

机译：乳酸乳球菌中高亲和力甜菜碱摄取系统（BusA）的遗传和生化表征揭示了细菌ABC转运蛋白中的新功能组织。

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The cytoplasmic accumulation of exogenous betaine stimulates the growth of Lactococcus lactis cultivated under hyperosmotic conditions. We report that L. lactis possesses a single betaine transport system that belongs to the ATP-binding cassette (ABC) superfamily of transporters. Through transposon mutagenesis, a mutant deficient in betaine transport was isolated. We identified two genes, busAA and busAB, grouped in an operon, busA (betaine uptake system). The transcription of busA is strongly regulated by the external osmolality of the medium. The busAA gene codes for the ATP-binding protein. busAB encodes a 573-residue polypeptide which presents two striking features: (i) a fusion between the regions encoding the transmembrane domain (TMD) and the substrate-binding domain (SBD) and (ii) a swapping of the SBD subdomains when compared to the Bacillus subtilisbetaine-binding protein, OpuAC. BusA of L. lactis displays a high affinity towards betaine (Km = 1.7 μM) and is an osmosensor whose activity is tightly regulated by external osmolality, leading the betaine uptake capacity ofL. lactis to be under dual control at the biochemical and genetic levels. A protein presenting the characteristics predicted for BusAB was detected in the membrane fraction of L. lactis. The fusion between the TMD and the SBD is the first example of a new organization within prokaryotic ABC transporters.
机译：外源甜菜碱的胞质积累刺激了高渗条件下培养的乳酸乳球菌的生长。我们报告该 L。乳酸具有单一的甜菜碱转运系统，属于转运蛋白ATP结合盒（ABC）超家族。通过转座子诱变，分离出甜菜碱运输缺陷的突变体。我们鉴定了两个基因，即 busAA 和 busAB ，它们被归入操纵子 busA （甜菜碱摄取系统）中。 busA 的转录受到培养基的外部渗透压的强烈调节。 busAA 基因编码ATP结合蛋白。 busAB 编码573个残基的多肽，具有两个显着特征：（i）编码跨膜结构域（TMD）和底物结合结构域（SBD）的区域之间的融合，以及（ii）交换与枯草芽孢杆菌甜菜碱结合蛋白OpuAC相比，SBD亚域的表达L的BusA。乳酸对甜菜碱显示出高亲和力（ K m = 1.7μM），是一种渗透压传感器，其活性受到外部渗透压的严格调节，导致甜菜碱的吸收能力的 L。乳酸菌在生化和遗传水平上都处于双重控制之下。在 L的膜级分中检测到了具有BusAB预测特征的蛋白质。乳酸。 TMD和SBD之间的融合是原核ABC转运蛋白中新组织的第一个例子。

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