Laboratoire de Recherche en Sciences Végétales, Université de Toulouse, CNRS, UPS, 31320 Auzeville Tolosane, France.
Paris-Lodron-University of Salzburg, Department of Biosciences, Salzburg 5020, Austria.
Int J Mol Sci. 2020 Apr 3;21(7):2488. doi: 10.3390/ijms21072488.
Plant cell wall proteins play major roles during plant development and in response to environmental cues. A bioinformatic search for functional domains has allowed identifying the PAC domain (Proline-rich, Arabinogalactan proteins, conserved Cysteines) in several proteins (PDPs) identified in cell wall proteomes. This domain is assumed to interact with pectic polysaccharides and -glycans and to contribute to non-covalent molecular scaffolds facilitating the remodeling of polysaccharidic networks during rapid cell expansion. In this work, the characteristics of the PAC domain are described in detail, including six conserved Cys residues, their spacing, and the predicted secondary structures. Modeling has been performed based on the crystal structure of a PAC domain. The presence of β-sheets is assumed to ensure the correct folding of the PAC domain as a β-barrel with loop regions. We show that PDPs are present in early divergent organisms from the green lineage and in all land plants. PAC domains are associated with other types of domains: Histidine-rich, extensin, Proline-rich, or yet uncharacterized. The earliest divergent organisms having PDPs are Bryophytes. Like the complexity of the cell walls, the number and complexity of PDPs steadily increase during the evolution of the green lineage. The association of PAC domains with other domains suggests a neo-functionalization and different types of interactions with cell wall polymers.
植物细胞壁蛋白在植物发育过程中以及对环境信号的响应中发挥着重要作用。通过生物信息学搜索功能域，在细胞壁蛋白质组中鉴定到的几种蛋白质（PDPs）中发现了 PAC 结构域（富含脯氨酸、阿拉伯半乳聚糖蛋白，保守半胱氨酸）。该结构域假定与果胶多糖和糖蛋白相互作用，并有助于非共价分子支架的形成，促进多糖网络在快速细胞扩张过程中的重塑。在这项工作中，详细描述了 PAC 结构域的特征，包括六个保守半胱氨酸残基、它们的间距和预测的二级结构。基于 PAC 结构域的晶体结构进行了建模。假定β-折叠的存在确保了 PAC 结构域正确折叠成具有环区的β-桶。我们表明，PDPs 存在于绿色谱系的早期分歧生物和所有陆地植物中。PAC 结构域与其他类型的结构域相关：富含组氨酸、伸展蛋白、富含脯氨酸或尚未表征。具有 PDPs 的最早分歧生物是苔藓植物。与细胞壁的复杂性一样，PDPs 的数量和复杂性在绿色谱系的进化过程中稳步增加。PAC 结构域与其他结构域的关联表明了新的功能化和与细胞壁聚合物的不同类型的相互作用。
