Benchabane H, Lortie L-A, Buckley N D, Trahan L, Frenette M
Groupe de Recherche en Ecologie Buccale, Département de Biochimie et Microbiologie (Sciences) and Faculté de Médecine Dentaire, Université Laval, Quebec City, Quebec, Canada, G1K 7P4.
J Dent Res. 2002 Jun;81(6):380-6. doi: 10.1177/0810380.
Xylitol is transported by Streptococcus mutans via a constitutive phosphoenolpyruvate:fructose phosphotransferase system (PTS) composed of a IIABC protein. Spontaneous xylitol-resistant strains are depleted in constitutive fructose-PTS activity, exhibit additional phenotypes, and are associated with the caries-preventive properties of xylitol. Polymerase chain-reactions and chromosome walking were used to clone the fxp operon that codes for the constitutive fructose/xylitol-PTS. The operon contained three open reading frames: fxpA, which coded for a putative regulatory protein of the deoxyribose repressor (DeoR) family, fxpB, which coded for a 1-phosphofructokinase, and fxpC, which coded for a IIABC protein of the fructose-PTS family. Northern blot analysis revealed that these genes were co-transcribed into a 4.4-kb mRNA even in the absence of fructose. Inactivation of the fxpC gene conferred resistance to xylitol, confirming its function. The fxp operon is also present in the genomes of other xylitol-sensitive streptococci, which could explain their sensitivity to xylitol.
木糖醇通过变形链球菌经由由IIABC蛋白组成的组成型磷酸烯醇丙酮酸：果糖磷酸转移酶系统（PTS）进行转运。自发的木糖醇抗性菌株的组成型果糖-PTS活性降低，表现出其他表型，并且与木糖醇的防龋特性相关。使用聚合酶链反应和染色体步移法克隆了编码组成型果糖/木糖醇-PTS的fxp操纵子。该操纵子包含三个开放阅读框：fxpA，编码假定的脱氧核糖阻遏物（DeoR）家族调节蛋白；fxpB，编码1-磷酸果糖激酶；fxpC，编码果糖-PTS家族的IIABC蛋白。Northern印迹分析表明，即使在没有果糖的情况下，这些基因也被共转录成4.4 kb的mRNA。fxpC基因的失活赋予了对木糖醇的抗性，证实了其功能。fxp操纵子也存在于其他木糖醇敏感链球菌的基因组中，这可以解释它们对木糖醇的敏感性。
