Title:Structure-function analysis of EFF-1 mediated cell-cell fusion
Cell-cellfusion is a universal multi-step process essential for organogenesis and sexualreproduction. EFF-1 protein and its paralog AFF-1 are necessary and sufficientfor fusion in the nematode Caenorhabditis elegans and in heterologoussystems. EFF-1 crystal structure showed that it is a homotrimer, structurallysimilar to viral class II fusion proteins (e.g. from Zika, Semliki Forest andDengue viruses). However, the mechanisms of EFF-1 and AFF-1-mediated cell-cellfusion remain elusive. Therefore, to achieve better understanding of themechanism of action, the focus of my research was EFF-1 and AFF-1oligomerization dynamics on the plasma membrane. My hypothesis was thattrimerization is a step required for the fusogenic activity of the proteins. Totest this hypothesis, I applied biochemical methods, such as surfacebiotinylation, and sucrose gradients as well as infections of AFF-1 andEFF-1-coated pseudotyped viruses. I found that A. Wild type EFF-1 ismostly trimeric on the surface of cells. B. The trimerization of EFF-1can be prevented in the presence of two independent point mutations, without areduction in protein activity. C. AFF-1 showed different oligomericstates on the plasma membrane. Based on these results I suggest a new model inwhich the monomer, and not the trimer, constitutes the active form of theseeukaryotic fusogens.