Graduate School of Science, Osaka City University, Osaka, 558-8585, Japan.
The OCU Advanced Research Institute for Natural Science and Technology (OCARINA), Osaka City University, Osaka, 558-8585, Japan.
FEMS Microbiol Lett. 2019 Feb 1;366(3). doi: 10.1093/femsle/fnz016.
Sialic acids, terminal structures of sialylated glycoconjugates, are widely distributed in animal tissues and are often involved in intercellular recognitions, including some bacteria and viruses. Mycoplasma mobile, a fish pathogenic bacterium, binds to sialyloligosaccharide (SO) through adhesin Gli349 and glides on host cell surfaces. The amino acid sequence of Gli349 shows no similarity to known SO-binding proteins. In the present study, we predicted the binding part of Gli349, produced it in Escherichia coli and proved its binding activity to SOs of fetuin using atomic force microscopy. Binding was detected with a frequency of 10.3% under retraction speed of 400 nm/s and was shown to be specific for SO, as binding events were competitively inhibited by the addition of free 3'-sialyllactose. The histogram of the unbinding forces showed 24 pN and additional peaks. These results suggested that the distal end of Gli349 constitutes a novel sialoadhesin domain and is directly involved in the gliding mechanism of M. mobile.
唾液酸是唾液酸化糖缀合物的末端结构，广泛分布于动物组织中，常参与细胞间识别，包括某些细菌和病毒。黏附素 Gli349 介导黏附性鱼病病原菌摩氏摩根菌（Mycoplasma mobile）与唾液酸化低聚糖（SO）结合并在宿主细胞表面滑行。Gli349 的氨基酸序列与已知的 SO 结合蛋白没有相似性。本研究预测了 Gli349 的结合部位，在大肠杆菌中进行表达，并使用原子力显微镜证明了其与胎球蛋白 SO 的结合活性。在回缩速度为 400nm/s 的情况下，检测到结合的频率为 10.3%，并且结合是特异性的，因为游离 3'-唾液乳糖的加入可以竞争性抑制结合事件。解附力的直方图显示了 24pN 和附加峰。这些结果表明，Gli349 的远端构成了一个新的唾液酸结合结构域，并直接参与 M. mobile 的滑行机制。
