In search of a ligand: What molecule activates receptor kinase SIRK1?

植物作为固着生物能够在整个昼夜循环中迅速适应变化的环境条件。在植物中，环境和发育信号的整合通常由受体激酶控制。受体激酶家族是植物激酶组中最大的分支，由超过600个成员组成。这些受体激酶被不同类型的配体激活，例如碳水化合物、固醇或各种类型的小肽。在过去的几年中，我们的小组已经将SIRK1表征为在外部蔗糖可用性改变下激活的受体激酶，但是作为SIRK1配体的分子仍然未知。该项目的主要目的是鉴定可以作为受体激酶SIRK1和辅助受体SAK1的配体的候选分子。在拟议的实验中，我们将使用不同的方法来识别潜在的配体分子。因此，我们（i）将使用生物化学方法分级分离低分子量蛋白质组分，并结合激酶活性测定，（ii）受体与已知配体和SIRK1的嵌合体，以确认候选配体的活性。假设肽可以根据配体分子，（iii）枯草杆菌酶敲除突变体的研究可能会让人们深入了解推定的肽配体的生物成因。在一个互补的方法将（四）寻找假定的配体上的碳水化合物微阵列。总的来说，该项目将使我们能够确定一个新的配体的受体激酶参与调节蔗糖诱导的反应。

Plants as sessile organisms are able to rapidly adapt to altering environmental conditions throughout the diurnal cycle. The integration of environmental and developmental signals in plants is often controlled by receptor kinases. The family of receptor kinases is the largest clade within the plant kinome consisting of over 600 members. These receptor kinases are activated by different types of ligands, such as carbohydrates, sterols or various types of small peptides. In the past years our group has characterized SIRK1 as a receptor kinase activated under alterations in external sucrose availability, but the molecule acting as a ligand to SIRK1 remains unknown. The major aim of this project is to identify candidate molecules that could act as a ligand to the receptor kinase SIRK1 and co-receptor SAK1. In the proposed experiments, we will use different approaches to identify potential ligand molecules. Thereby, we (i) will use biochemical methods fractionating low molecular weight protein components coupled to kinase activity assays, (ii) chimera of a receptor with known ligand and SIRK1 to confirm activity of the ligand candidates. Under the assumption that peptides could be under the ligand molecules, (iii) the study of subtilase knock-out mutants may give insights into the biogenesis of putative peptide ligands. In a complementary approach will (iv) search for putative ligands on a carbohydrate microarrays. Overall, the project will allow us to identify a new ligand for a receptor kinase involved in regulation of sucrose-induced responses.