DsdX is the second D-serine transporter in uropathogenic Escherichia coli clinical isolate CFT073
DsdX is the second D-serine transporter in uropathogenic Escherichia coli clinical isolate CFT073
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DOI：
10.1128/jb.00634-06
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发表时间：
2006-09-01
影响因子：
3.2
通讯作者：
Welch, Rodney A.
中科院分区：
文献类型：
--
作者：
Anfora, Andrew T.;Welch, Rodney A.
D-丝氨酸是哺乳动物尿液中存在的一种氨基酸，对缺乏功能性dsdA基因的大肠杆菌菌株具有抑制作用。与直觉相反，E.大肠杆菌临床分离株CFT 073在泌尿道感染的鼠模型中的共感染期间相对于野生型过度定殖小鼠的膀胱和肾脏。我们对CFT 073中D-丝氨酸的摄取机制感兴趣。D-丝氨酸进入E. coli K-12中通过CycA、D-丙氨酸转运蛋白和D-环丝氨酸敏感性位点的表达。CFT 073 cycA可以在以D-丝氨酸作为唯一碳源的基本培养基上生长。dsdCXA基因座的dsdX基因是基于其预测的氨基酸序列与葡萄糖酸盐转运蛋白的相似性的额外D-丝氨酸转运蛋白的可能候选者。在基本培养基中，CFT 073 dsdX可以在D-丝氨酸作为唯一碳源上生长;然而，CFT 7073 dsdX cycA不能。此外，在甘油和D-丝氨酸基本培养基上生长期间，CFT 073 dsdXA cycA对D-丝氨酸的抑制浓度不敏感。用携带dsdX或cycA重组质粒的CFT 073 dsdX cycA进行的D-[C-14]丝氨酸摄取实验证实D-丝氨酸能够进入E. coli细胞中进行表达。在全细胞D- [C-14]丝氨酸摄取实验中，DsdX具有58.75 μ M的表观K-m和75.96 nmol/min/mg的V-max，CycA具有82.40 μ M的表观K-m和58.90 nmol/min/mg的V-max。只有D-苏氨酸略微抑制DsdX介导的D-丝氨酸转运，而D-丙氨酸、甘氨酸和D-环丝氨酸抑制CycA介导的D-丝氨酸转运。DsdX或CycA足以运输生理量的D-丝氨酸，但DsdX是D-丝氨酸特异性通透酶。
D-Serine is an amino acid present in mammalian urine that is inhibitory to Escherichia coli strains lacking a functional dsdA gene. Counterintuitively, a dsd4 strain of E. coli clinical isolate CFT073 hypercolonizes the bladder and kidneys of mice relative to wild type during a coinfection in the murine model of urinary tract infection. We are interested in the mechanisms for uptake Of D-serine in CFT073. D-Serine enters E. coli K-12 via CycA, the D-alanine transporter and D-cycloserine sensitivity locus. CFT073 cycA can grow on minimal medium with D-serine as a sole carbon source. The dsdX gene of the dsdCXA locus is a likely candidate for an additional D-serine transporter based on its predicted amino acid sequence similarity to gluconate transporters. In minimal medium, CFT073 dsdX can grow on D-serine as a sole carbon source; however, CFT7073 dsdX cycA cannot. Additionally, CFT073 dsdXA cycA is not sensitive to inhibitory concentrations Of D-serine during growth on glycerol and D-serine minimal medium. D-[C-14] serine uptake experiments with CFT073 dsdX cycA harboring dsdX or cycA recombinant plasmids confirm that D-serine is able to enter E. coli cells via CycA or DsdX. In whole-Cell D- [C-14] serine uptake experiments, DsdX has an apparent K-m of 58.75 mu M and a V-max Of 75.96 nmol/min/mg, and CycA has an apparent K-m of 82.40 mu M and a V-max of 58.90 nmol/min/mg. Only D-threonine marginally inhibits DsdX-mediated D-serine transport, whereas D-alanine, glycine, and D-Cycloserine inhibit CycA-mediated D-serine transport. DsdX or CycA is sufficient to transport physiological quantities of D-serine, but DsdX is a D-serine-specific permease.