Monedero Vicente, Yebra María Jesús, Poncet Sandrine, Deutscher Josef
Laboratorio de Bacterias Lácticas y Probióticos, IATA-CSIC, P.O. Box 73, 46100 Burjassot, Valencia, Spain.
Res Microbiol. 2008 Mar;159(2):94-102. doi: 10.1016/j.resmic.2007.10.002. Epub 2007 Nov 4.
Transport of maltose in Lactobacillus casei BL23 is subject to regulation by inducer exclusion. The presence of glucose or other rapidly metabolized carbon sources blocks maltose transport by a control mechanism that depends on the phosphorylation of the HPr protein at serine residue 46. We have identified the L. casei gene cluster for maltose/maltodextrin utilization by sequence analysis and mutagenesis. It is composed of genes coding for a transcriptional regulator, oligosaccharide hydrolytic enzymes, an ABC transporter (MalEFGK2) and the enzymes for the metabolism of maltose or the degradation products of maltodextrins: maltose phosphorylase and beta-phospho-glucomutase. These genes are induced by maltose and repressed by the presence of glucose via the catabolite control protein A (CcpA). A mutant strain was constructed which expressed the hprKV267F allele and therefore formed large amounts of P-Ser-HPr even in the absence of a repressive carbon source. In this mutant, transport of maltose was severely impaired, whereas transport of sugars not subject to inducer exclusion was not changed. These results strengthen the idea that P-Ser-HPr controls inducer exclusion and make the maltose system of L. casei a suitable model for studying this process in Firmicutes.
干酪乳杆菌BL23中麦芽糖的转运受诱导物排除调节。葡萄糖或其他快速代谢的碳源的存在通过一种依赖于HPr蛋白丝氨酸残基46磷酸化的控制机制来阻断麦芽糖转运。我们通过序列分析和诱变鉴定了干酪乳杆菌利用麦芽糖/麦芽糊精的基因簇。它由编码转录调节因子、寡糖水解酶、ABC转运蛋白（MalEFGK2）以及麦芽糖代谢或麦芽糊精降解产物代谢的酶（麦芽糖磷酸化酶和β-磷酸葡萄糖变位酶）的基因组成。这些基因由麦芽糖诱导，并通过分解代谢物控制蛋白A（CcpA）在葡萄糖存在时被抑制。构建了一个表达hprKV267F等位基因的突变菌株，因此即使在没有抑制性碳源的情况下也能形成大量的P-Ser-HPr。在这个突变体中，麦芽糖的转运严重受损，而不受诱导物排除影响的糖的转运没有变化。这些结果强化了P-Ser-HPr控制诱导物排除的观点，并使干酪乳杆菌的麦芽糖系统成为研究厚壁菌门中这一过程的合适模型。
