Zhuang Lei, Trueb Beat
Department of Clinical Research, University of Bern, 3008 Bern, Switzerland.
Department of Clinical Research, University of Bern, 3008 Bern, Switzerland; Department of Rheumatology, University Hospital, 3010 Bern, Switzerland.
Arch Biochem Biophys. 2017 Jul 1;625-626:54-64. doi: 10.1016/j.abb.2017.06.002. Epub 2017 Jun 5.
FGFRL1 is a transmembrane receptor that can induce the fusion of CHO cells to multinucleated syncytia. This cell fusion activity has been attributed to the extracellular Ig3 domain of the receptor. We investigated how the fusogenic activity evolved during the evolution of animals. We found that the Ig3 domain from humans, mice, chicken and fish stimulates fusion of CHO cells, while the Ig3 domain from lancelet and sea urchin does not. It is therefore conceivable that the fusogenic activity of FGFRL1 developed during the evolution of vertebrates. Bony fish contain two copies of the FGFRL1 gene because they have undergone a whole-genome duplication. One of the corresponding proteins (FGFRL1a) induces cell-cell fusion, while the other (FGFRL1b) does not. Analysis of chimeric constructs and in vitro mutagenesis suggested that FGFRL1b has lost its fusogenic activity after duplication. A rescue experiment supported this conclusion. When four amino acids were changed, the Ig3 domain of FGFRL1b was converted into an active, fusogenic protein comparable to FGFRL1a. The four amino acids are located in a hydrophobic pocket of the Ig3 domain. It is likely that this hydrophobic pocket interacts with a target molecule on the membrane of adjacent cells to induce cell-cell fusion.
FGFRL1是一种跨膜受体，能够诱导CHO细胞融合形成多核合胞体。这种细胞融合活性归因于该受体的细胞外Ig3结构域。我们研究了动物进化过程中促融合活性是如何演变的。我们发现，来自人类、小鼠、鸡和鱼的Ig3结构域能刺激CHO细胞融合，而来自文昌鱼和海胆的Ig3结构域则不能。因此可以推测，FGFRL1的促融合活性是在脊椎动物进化过程中产生的。硬骨鱼含有两个FGFRL1基因拷贝，因为它们经历了一次全基因组复制。其中一个相应的蛋白质（FGFRL1a）能诱导细胞间融合，而另一个（FGFRL1b）则不能。对嵌合构建体的分析和体外诱变表明，FGFRL1b在复制后失去了促融合活性。一项拯救实验支持了这一结论。当四个氨基酸发生改变时，FGFRL1b的Ig3结构域就会转化为一种与FGFRL1a相当的具有活性的促融合蛋白。这四个氨基酸位于Ig3结构域的一个疏水口袋中。很可能这个疏水口袋与相邻细胞膜上的一个靶分子相互作用，从而诱导细胞间融合。
