Regulation Of Sugar Transport And Metabolism In Lactic A

膳食中的蔗糖是口腔细菌致病性的主要因素。例如，在龋齿的病因学中：(1)蔗糖为多糖的合成提供了基础，从而促进了链球菌物种对牙齿表面的粘附；(2)糖的细菌发酵产生乳酸，导致牙釉质脱矿。蔗糖本身由葡萄糖和果糖分子组成，它们连接在前者的碳原子1和后者的碳原子2之间。蔗糖在转运到细菌的同时被磷酸化，随后被一种称为蔗糖6-磷酸水解酶（S6PH）的酶水解。葡萄糖的C1和果糖的剩余5个碳原子之间的葡萄糖基键的修饰产生5种蔗糖类似物：海藻糖（1-1）、土聚糖（1-3）、麦芽糖（1-4）、亮糖（1-5）和巴氏糖（1-6）。与蔗糖相反，这些同分异构体化合物不支持口腔微生物的生长，包括链球菌。这些相对甜的类似物中的两种（巴氏糖和亮糖）已在工业规模上生产，由于它们的无龋齿性，是膳食蔗糖的潜在替代品。一般认为微生物不能代谢蔗糖的五种异构体。然而，我们过去一年的研究需要对这一假设进行重新评估，因为我们发现包括克雷伯氏菌、梭菌、梭杆菌和芽胞杆菌在内的一些物种能够利用这些碳水化合物作为生长的能量来源。鉴定了异构化合物同化所需的相关基因和操纵子，并对其编码酶进行了表达、纯化和表征。我们的研究表明，这些基因不存在于口腔链球菌的基因组中，从而为变形链球菌等生物体无法代谢蔗糖异构体提供了合理的解释。其他主要成就包括首次生物合成蔗糖的五种磷酸化异构体，并证明蔗糖-6-磷酸水解酶不能催化任何这些磷酸化衍生物的水解。这些磷酸化的α连接的化合物将被用于尝试结晶参与其水解的糖基水解酶。在相关实验中，从肺炎克雷伯菌中纯化了一种新的atp依赖性β -葡萄糖苷激酶（BglK），并利用该酶制备了相应的磷酸化β -连接化合物。这些研究结果发表在最近一期的《生物化学与碳水化合物研究》杂志上。我们的发现可能为蔗糖类似物的合成提供了新的思路，这些类似物可能允许选择性靶向和抑制引起龋齿的细菌，如变形链球菌和sobrinus链球菌的生长。

Dietary sucrose is a major contributor to pathogenicity of oral bacteria. For example, in the etiology of dental caries : (1) sucrose provides the building blocks for synthesis of glycans that facilitate adherence of Streptococcal species to the tooth surface, and (2) bacterial fermentation of the sugar generates lactic acid that causes demineralization of tooth enamel. Sucrose itself comprises glucose and fructose molecules that are linked between carbon atom 1 of the former and carbon atom 2 of the latter. Sucrose is phosphorylated simultaneously with transport into the bacteria, where it is subsequently hydrolyzed by an enzyme designated sucrose 6-phosphate hydrolase (S6PH). Modification of the glucosyl- linkages between C1 of glucose and the remaining five carbon atoms of fructose yield five analogs of sucrose designated : trehalulose (1-1), turanose (1-3), maltulose (1-4), leucrose (1-5) and palatinose (1-6).In contrast to sucrose, the isomeric compounds do not support growth of oral microorganisms, including streptococcal species. Two of these relatively sweet analogs (palatinose and leucrose) are produced on an industrial scale and - by virtue of their non-cariogenicity - are potential substitutes for dietary sucrose. It has generally been assumed that microorganisms are unable to metabolize the five isomers of sucrose. However, our studies of the past year necessitate a re-evaluation of this assumption, by the finding that several species including Klebsiella, Clostridia, Fusobacteria and Bacilli are able to use these carbohydrates as energy sources for growth. The relevant genes and operons required for the disimilation of the isomeric compounds have been identified, and the encoded enzymes have been expressed, purified and characterized. Our studies show that these genes are not present in the genomes of the oral streptococci, and thus provide a rational explanation for the inability of organisms such as Streptococcus mutans to metabolize the sucrose isomers. Other major accomplishments included the first biosynthesis of the five phosphorylated isomers of sucrose, and the demonstration that sucrose-6-phosphate hydrolase is unable to catalyze the hydrolysis of any of these phosphorylated derivatives. These phosphorylated alpha-linked compounds will be used in attempts to crystallize the glycosylhydrolase enzymes that participate in their hydrolysis. In related experiments, a novel ATP-dependent beta glucoside kinase (BglK) has been purified from Klebsiella pneumoniae, and this enzyme has been used to prepare the corresponding phosphorylated beta-linked compounds.These results have been published in recent issues of the Journal of Biological Chemistry and Carbohydrate Research. Our findings may provide insight to the for the synthesis of sucrose analogs that may permit selective targeting and inhibition of growth of caries-inducing bacteria such as Streptococcus mutans and Streptococcus sobrinus.