State Key Laboratory of Agrobiotechnology, China Agricultural University, Beijing, China.
PLoS One. 2013 Jul 2;8(7):e67477. doi: 10.1371/journal.pone.0067477. Print 2013.
The phytohormone abscisic acid ((+)-ABA) plays a key role in many processes. The biological and biochemical activities of unnatural (-)-ABA have been extensively investigated since 1960s. However, the recognition mechanism by which only a few members among PYR/PYL/RCAR (PYLs) family can bind (-)-ABA remains largely unknown. Here we systematically characterized the affinity of PYLs binding to the (-)-ABA and reported the crystal structures of apo-PYL5, PYL3-(-)-ABA and PYL9-(+)-ABA. PYL5 showed the strongest binding affinity with (-)-ABA among all the PYLs. PYL9 is a stringently exclusive (+)-ABA receptor with interchangeable disulfide bonds shared by a subclass of PYLs. PYL3 is a dual receptor to both ABA enantiomers. The binding orientation and pocket of (-)-ABA in PYLs are obviously different from those of (+)-ABA. Steric hindrance and hydrophobic interaction are the two key factors in determining the stereospecificity of PYLs binding to (-)-ABA, which is further confirmed by gain-of-function and loss-of-function mutagenesis. Our results provide novel insights of the bioactivity of ABA enantiomers onto PYLs, and shed light on designing the selective ABA receptors agonists.
植物激素脱落酸（(+)-ABA）在许多过程中起着关键作用。自 20 世纪 60 年代以来，人们对非天然（-)-ABA 的生物和生化活性进行了广泛的研究。然而，只有少数 PYR/PYL/RCAR（PYLs）家族成员能够结合（-)-ABA 的识别机制在很大程度上仍然未知。在这里，我们系统地表征了 PYLs 与（-)-ABA 的结合亲和力，并报告了 apo-PYL5、PYL3-(-)-ABA 和 PYL9-(+)-ABA 的晶体结构。在所有 PYLs 中，PYL5 与（-)-ABA 具有最强的结合亲和力。PYL9 是一个严格排他的（+)-ABA 受体，具有由亚类 PYLs 共享的可互换二硫键。PYL3 是两种 ABA 对映体的双重受体。（-)-ABA 在 PYLs 中的结合取向和口袋明显不同于（+)-ABA。空间位阻和疏水相互作用是决定 PYLs 对（-)-ABA 立体特异性的两个关键因素，这进一步通过功能获得和功能丧失突变得到证实。我们的研究结果为 ABA 对映体对 PYLs 的生物活性提供了新的见解，并为设计选择性 ABA 受体激动剂提供了思路。
