Graduate School of Natural Science and Technology, Okayama University, Tsushima-naka 1-1-1, Kita-ku, Okayama 700-8530, Japan.
Mol Plant Pathol. 2012 Sep;13(7):764-74. doi: 10.1111/j.1364-3703.2012.00789.x. Epub 2012 Feb 21.
Type IV pilin (PilA) is a major constituent of pilus and is required for bacterial biofilm formation, surface motility and virulence. It is known that mature PilA is produced by cleavage of the short leader sequence of the pilin precursor, followed by methylation of N-terminal phenylalanine. The molecular mass of the PilA mature protein from the tobacco bacterial pathogen Pseudomonas syringae pv. tabaci 6605 (Pta 6605) has been predicted to be 12 329 Da from its deduced amino acid sequence. Previously, we have detected PilA as an approximately 13-kDa protein by immunoblot analysis with anti-PilA-specific antibody. In addition, we found the putative oligosaccharide-transferase gene tfpO downstream of pilA. These findings suggest that PilA in Pta 6605 is glycosylated. The defective mutant of tfpO (ΔtfpO) shows reductions in pilin molecular mass, surface motility and virulence towards host tobacco plants. Thus, pilin glycan plays important roles in bacterial motility and virulence. The genetic region around pilA was compared among P. syringae pathovars. The tfpO gene exists in some strains of pathovars tabaci, syringae, lachrymans, mori, actinidiae, maculicola and P. savastanoi pv. savastanoi. However, some strains of pathovars tabaci, syringae, glycinea, tomato, aesculi and oryzae do not possess tfpO, and the existence of tfpO is independent of the classification of pathovars/strains in P. syringae. Interestingly, the PilA amino acid sequences in tfpO-possessing strains show higher homology with each other than with tfpO-nonpossessing strains. These results suggest that tfpO and pilA might co-evolve in certain specific bacterial strains.
IV 型菌毛蛋白（PilA）是菌毛的主要成分，对于细菌生物膜形成、表面运动和毒力是必需的。已知成熟的 PilA 是由菌毛前体的短引导序列切割产生的，然后 N 端苯丙氨酸被甲基化。来自烟草细菌性病原体丁香假单胞菌 pv. tabaci 6605（Pta 6605）的 PilA 成熟蛋白的分子质量已根据其推导的氨基酸序列预测为 12329 Da。以前，我们通过用抗 PilA 特异性抗体进行免疫印迹分析检测到 PilA 约为 13 kDa 的蛋白。此外，我们发现 pilA 下游有一个推定的寡糖转移酶基因 tfo。这些发现表明 Pta 6605 中的 PilA 是糖基化的。tfpO （ΔtfpO）的缺陷突变体表现出菌毛分子质量降低、表面运动性降低以及对宿主烟草植物的毒力降低。因此，菌毛聚糖在细菌运动性和毒力中发挥重要作用。在丁香假单胞菌的不同致病型之间比较了 pilA 周围的遗传区域。tfpO 基因存在于一些致病型 tabaci、syringae、lachrymans、mori、actinidiae、maculicola 和 P. savastanoi pv. savastanoi 的菌株中。然而，一些致病型 tabaci、syringae、glycinea、tomato、aesculi 和 oryzae 的菌株不具有 tfo，并且 tfo 的存在与丁香假单胞菌的致病型/菌株分类无关。有趣的是，具有 tfo 的菌株中的 PilA 氨基酸序列彼此之间的同源性高于不具有 tfo 的菌株。这些结果表明，tfo 和 pilA 可能在某些特定的细菌菌株中共同进化。
