Alexander Candace R, Dingman Douglas W, Schultes Neil P, Mourad George S
Department of Biology, Indiana University-Purdue University Fort Wayne, 2101 East Coliseum Blvd., Fort Wayne, IN 46805, USA.
Department of Entomology, The Connecticut Agricultural Experiment Station, 123 Huntington St, New Haven, CT 06511, USA.
FEMS Microbiol Lett. 2018 Apr 1;365(7). doi: 10.1093/femsle/fny018.
Two nucleobase transporters encoded in the genome of the Honey bee bacterial pathogen Paenibacillus larvae belong to the azaguanine-like transporters and are referred to as PlAzg1 and PlAzg2. PlAzg1 and 2 display significant amino acid sequence similarity, and share predicted secondary structures and functional sequence motifs with two Escherichia coli nucleobase cation symporter 2 (NCS2) members: adenine permease (EcAdeP) and guanine-hypoxanthine permease EcGhxP. However, similarity does not define function. Heterologous complementation and functional analysis using nucleobase transporter-deficient Saccharomyces cerevisiae strains revealed that PlAzg1 transports adenine, hypoxanthine, xanthine and uracil, while PlAzg2 transports adenine, guanine, hypoxanthine, xanthine, cytosine and uracil. Both PlAzg1 and 2 display high affinity for adenine with Km of 2.95 ± 0.22 and 1.92 ± 0.22 μM, respectively. These broad nucleobase transport profiles are in stark contrast to the narrow transport range observed for EcAdeP (adenine) and EcGhxP (guanine and hypoxanthine). PlAzg1 and 2 are similar to eukaryotic Azg-like transporters in that they share a broad solute transport profile, particularly the fungal Aspergillus nidulans AzgA (that transports adenine, guanine and hypoxanthine) and plant AzgA transporters from Arabidopsis thaliana and Zea mays (that collectively move adenine, guanine, hypoxanthine, xanthine, cytosine and uracil).
蜜蜂细菌性病原菌幼虫芽孢杆菌基因组中编码的两种核碱基转运蛋白属于氮杂鸟嘌呤样转运蛋白，分别称为PlAzg1和PlAzg2。PlAzg1和PlAzg2显示出显著的氨基酸序列相似性，并与两种大肠杆菌核碱基阳离子同向转运蛋白2（NCS2）成员：腺嘌呤通透酶（EcAdeP）和鸟嘌呤 - 次黄嘌呤通透酶EcGhxP共享预测的二级结构和功能序列基序。然而，相似性并不决定功能。使用缺乏核碱基转运蛋白的酿酒酵母菌株进行的异源互补和功能分析表明，PlAzg1转运腺嘌呤、次黄嘌呤、黄嘌呤和尿嘧啶，而PlAzg2转运腺嘌呤、鸟嘌呤、次黄嘌呤、黄嘌呤、胞嘧啶和尿嘧啶。PlAzg1和PlAzg2对腺嘌呤均具有高亲和力，Km分别为2.95±0.22和1.92±0.22μM。这些广泛的核碱基转运谱与EcAdeP（腺嘌呤）和EcGhxP（鸟嘌呤和次黄嘌呤）观察到的狭窄转运范围形成鲜明对比。PlAzg1和PlAzg2与真核生物Azg样转运蛋白相似，因为它们具有广泛的溶质转运谱，特别是真菌构巢曲霉AzgA（转运腺嘌呤、鸟嘌呤和次黄嘌呤）以及来自拟南芥和玉米的植物AzgA转运蛋白（共同转运腺嘌呤、鸟嘌呤、次黄嘌呤、黄嘌呤、胞嘧啶和尿嘧啶）。
