The FKBP39 from Drosophila melanogaster is a multifunctional regulatory immunophilin. It contains two globular domains linked by a highly charged disordered region. The N-terminal domain shows homology to the nucleoplasmin core domain, and the C-terminal domain is characteristic for the family of the FKBP immunophilin ligand binding domain. The specific partially disordered structure of the protein inspired us to investigate whether FKBP39 can drive spontaneous liquid-liquid phase separation (LLPS). Preliminary analyses using CatGranule and Pi-Pi contact predictors suggested a propensity for LLPS. Microscopy observations revealed that FKBP39 can self-concentrate to form liquid condensates. We also found that FKBP39 can lead to LLPS in the presence of RNA and peptides containing Arg-rich linear motifs derived from selected nuclear and nucleolar proteins. These heterotypic interactions have a stronger propensity for driving LLPS when compared to the interactions mediated by self-associating FKBP39 molecules. To investigate whether FKBP39 can drive LLPS in the cellular environment, we analysed it in fusion with YFP in COS-7 cells. The specific distribution and diffusion kinetics of FKBP39 examined by FRAP experiments provided evidence that immunophilin is an important driver of phase separation. The ability of FKBP39 to go into heterotypic interaction may be fundamental for ribosome subunits assembly.

果蝇的FKBP39是多功能调节免疫亲和素。它包含两个球状结构域，由高电荷无序区连接。N端结构域显示出与核纤溶酶核心结构域的同源性，而C端结构域是FKBP亲免蛋白配体结合结构域家族的特征。该蛋白质的特定部分无序结构激发了我们研究FKBP39是否可以驱动自发性液-液相分离（LLPS）。使用CatGranule和Pi-Pi接触预测因子的初步分析表明LLPS的可能性很大。显微镜观察表明，FKBP39可以自浓缩形成液体冷凝物。我们还发现，在存在RNA和含有富含Arg的线性基序的肽和RNA的肽存在下，FKBP39可以导致LLPS，这些线性基序来源于选定的核蛋白和核仁蛋白。与通过自缔合的FKBP39分子介导的相互作用相比，这些异型相互作用具有更强的驱动LLPS的倾向。为了研究FKBP39是否可以在细胞环境中驱动LLPS，我们在COS-7细胞中与YFP融合对其进行了分析。FRAP实验检测的FKBP39的特定分布和扩散动力学提供了证据，表明亲免蛋白是相分离的重要驱动力。FKBP39进入异型相互作用的能力可能是核糖体亚基组装的基础。FRAP实验检查的FKBP39的特定分布和扩散动力学提供了证据，表明亲免素是相分离的重要驱动力。FKBP39进入异型相互作用的能力可能是核糖体亚基组装的基础。FRAP实验检测的FKBP39的特定分布和扩散动力学提供了证据，表明亲免蛋白是相分离的重要驱动力。FKBP39进入异型相互作用的能力可能是核糖体亚基组装的基础。